Bumps [heed](https://github.com/Kerollmops/heed) from 0.22.0 to 0.22.1. <details> <summary>Release notes</summary> Sourced from <a href="https://github.com/Kerollmops/heed/releases">heed's releases</a>. <blockquote> <h2>v0.22.1</h2>  This release brings a new functionality: the possibility to <a href="https://docs.rs/heed/latest/heed/struct.RwTxn.html#method.nested_read_txn">create multiple nested read transactions from an uncommitted write transaction</a>. You can also examine another usage in <a href="https://github.com/meilisearch/heed/blob/86cd1f681953cd5f6870706f6139b851e975975e/heed/examples/nested-rtxns.rs">the dedicated example file</a>. We finally merged the changes to upstream LMDB (mdb.master3), and the patch <a href="https://bugs.openldap.org/show_bug.cgi?id=10395">has been thoroughly reviewed by Howard Chu</a>. <pre lang="rust"><code>// opening a write transaction let mut wtxn = env.write_txn()?; // [use the RwTxn to write into the env] // opening multiple read-only transactions without committing beforehand let rtxns = (0..1000).map(|| env.nested_read_txn(&wtxn)).collect::<heed::Result<Vec<>>>()?; // you can also spawn nested read transactions from the write txn too let rtxns = (0..1000).map(|| wtxn.nested_read_txn()).collect::<heed::Result<Vec<>>>()?; // [use the RoTxns and move them onto different threads] </code></pre> <h2>v0.22.1-nested-rtxns</h2>  This release brings a new experimental functionality: the possibility to <a href="https://docs.rs/heed/0.22.1-nested-rtxns/heed/struct.Env.html#method.nested_read_txn">create multiple nested read transactions from an uncommitted write transaction</a>. You can also examine another usage in <a href="https://github.com/meilisearch/heed/blob/95a3907dfb686bf2f7f7455530bc30052d5c2937/heed/examples/nested-rtxns.rs">the dedicated example file</a> or in <a href="https://redirect.github.com/meilisearch/meilisearch/pull/5307">this Meilisearch pull request</a>. We are attempting to merge the necessary changes to upstream LMDB, but it will require additional work to ensure it produces correct C code. You can review <a href="https://bugs.openldap.org/show_bug.cgi?id=10395">the dedicated OpenLDAP tracking issue</a> to see how it progresses. <pre lang="rust"><code>// opening a write transaction let mut wtxn = env.write_txn()?; // [use the RwTxn to write into the env] // opening multiple read-only transactions without committing beforehand let rtxns = (0..1000).map(|| env.nested_read_txn(&wtxn)).collect::<heed::Result<Vec<>>>()?; // [use the RoTxns and move them onto different threads] </code></pre> <h2>v0.22.1-nested-rtxns-7</h2>  This release brings a new experimental functionality: the possibility to <a href="https://docs.rs/heed/0.22.1-nested-rtxns-7/heed/struct.Env.html#method.nested_read_txn">create multiple nested read transactions from an uncommitted write transaction</a>. You can also examine another usage in <a href="https://github.com/meilisearch/heed/blob/95a3907dfb686bf2f7f7455530bc30052d5c2937/heed/examples/nested-rtxns.rs">the dedicated example file</a> or in <a href="https://redirect.github.com/meilisearch/meilisearch/pull/5307">this Meilisearch pull request</a>. We are attempting to merge the necessary changes to upstream LMDB, but it will require additional work to ensure it produces correct C code. You can review <a href="https://bugs.openldap.org/show_bug.cgi?id=10395">the dedicated OpenLDAP tracking issue</a> to see how it progresses. The latest version of the LMDB is more stable, without memory leaks, and is capable of correctly interacting with the dirty pages list.  </blockquote> ... (truncated) </details> <details> <summary>Commits</summary> <ul> <li><a href="https://github.com/meilisearch/heed/commit/86cd1f681953cd5f6870706f6139b851e975975e"><code>86cd1f6</code></a> Merge pull request <a href="https://redirect.github.com/Kerollmops/heed/issues/307">#307</a> from meilisearch/allow-nested-rtxn-from-wtxn</li> <li><a href="https://github.com/meilisearch/heed/commit/ee7354979dddf729cfbfd7448ff5bf15f83b365e"><code>ee73549</code></a> Introduce the Env and RwTxn nested_read_txn methods to create nested rtxns</li> <li><a href="https://github.com/meilisearch/heed/commit/345db35d736769562fbd94b52a5e09996115eaee"><code>345db35</code></a> Merge pull request <a href="https://redirect.github.com/Kerollmops/heed/issues/357">#357</a> from shawn-willden-ai/no_std</li> <li><a href="https://github.com/meilisearch/heed/commit/5734bcf830a51ac5a92a1b1861b48a4555467e83"><code>5734bcf</code></a> Update bindgen and apply no_std to lmdb-master3-sys</li> <li><a href="https://github.com/meilisearch/heed/commit/9e94ed965d55b11994085f80178d393d8ec07ac2"><code>9e94ed9</code></a> Add no_std feature to lmdb-master-sys</li> <li><a href="https://github.com/meilisearch/heed/commit/1262931497fc9fd7d47f6834288bca8fae832d93"><code>1262931</code></a> Merge pull request <a href="https://redirect.github.com/Kerollmops/heed/issues/354">#354</a> from meilisearch/expose_env_stats</li> <li><a href="https://github.com/meilisearch/heed/commit/97c7f1261c91d1eaaf0951a6de99f8bec7b1f640"><code>97c7f12</code></a> Expose env stats</li> <li><a href="https://github.com/meilisearch/heed/commit/63fba6fe44ecf5278ce5a6a994c19d6976985b1b"><code>63fba6f</code></a> Merge pull request <a href="https://redirect.github.com/Kerollmops/heed/issues/353">#353</a> from Boog900/preserve-cmp</li> <li><a href="https://github.com/meilisearch/heed/commit/bf940e16c639904a04d096c0ef794be5053b270e"><code>bf940e1</code></a> preserve cmp functions with DatabaseOpenOptions::types</li> <li><a href="https://github.com/meilisearch/heed/commit/fdd105db2f48750a043b9df2b50744f886dbdd25"><code>fdd105d</code></a> Merge pull request <a href="https://redirect.github.com/Kerollmops/heed/issues/349">#349</a> from uniphil/patch-1</li> <li>Additional commits viewable in <a href="https://github.com/Kerollmops/heed/compare/v0.22.0...v0.22.1">compare view</a></li> </ul> </details> [![Dependabot compatibility score](https://dependabot-badges.githubapp.com/badges/compatibility_score?dependency-name=heed&package-manager=cargo&previous-version=0.22.0&new-version=0.22.1)](https://docs.github.com/en/github/managing-security-vulnerabilities/about-dependabot-security-updates#about-compatibility-scores) Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. 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