add hello-single-latest sync example

[harunugurlu]

Description

Adds hello-single-latest example demonstrating the SingleLatest buffer through AimDB's synchronous API.

The example:

• registers an f32 feature-flag record backed by BufferCfg::SingleLatest
• publishes rollout percentage updates using a synchronous SyncProducer
• observes updates through configured "fast" and "slow" taps
• documents the current-state semantics of SingleLatest
• adds the example to the workspace, Makefile, and main README

Related Issue

• Closes Add minimal example: hello-single-latest #93

Testing

The following commands completed successfully:

• cargo fmt --all -- --check
• cargo check -p hello-single-latest
• cargo clippy -p hello-single-latest --all-targets -- -D warnings
• cargo run -p hello-single-latest
• make examples

make check completed all preceding checks but failed at the existing codegen-drift step on macOS because of a BSD sed regular-expression compatibility error:

sed: RE error: invalid repetition count(s)
make: *** [codegen-drift] Error 1

Checklist

• I have read the [CONTRIBUTING.md](https://github.com/aimdb-dev/aimdb/blob/main/CONTRIBUTING.md) document.
• My code follows the project's coding standards.
• I have added tests to cover my changes. Not applicable: this PR adds a runnable documentation example rather than new library behavior.
• All new and existing tests passed (make check). The command is currently blocked by the macOS sed compatibility issue described above.
• I have updated the documentation accordingly.

[lxsaah]

Great iteration! The fast/slow taps demonstrate the SingleLatest coalescing cleanly and moving the delay/logging onto ctx is exactly right. Two small, optional polish suggestions inline:

[lxsaah]

Looks good. Thanks for your contribution!

[harunugurlu]

Hey @lxsaah thanks a lot for your feedbacks and approving the PR. I can't seem to merge it though, it says "Merging is blocked, Cannot change this locked branch". Am I missing something here, or I simply don't have the authorization to merge?

[lxsaah]

I merged the branch as there is authorization missing. Thanks again.