chore: update Rust toolchain to 1.96.0 (#22611)

## Which issue does this PR close?

<!-- No tracking issue; routine toolchain maintenance. -->

- Closes #.

## Rationale for this change

Keeps the pinned Rust toolchain current. This bumps the toolchain used
to
compile the workspace and run CI jobs from `1.95.0` to `1.96.0`.

## What changes are included in this PR?

- `rust-toolchain.toml`: bump `channel` from `1.95.0` to `1.96.0`.
- `docs/source/contributor-guide/development_environment.md`: update the
`rustup component add --toolchain 1.96.0 rust-analyzer` example to
match.

The MSRV (`rust-version = "1.88.0"` in the workspace `Cargo.toml`) is
unchanged.

## Are these changes tested?

Covered by existing CI, which compiles and lints the workspace with the
pinned toolchain. `cargo clippy --all-targets --all-features -- -D
warnings`
was run locally against 1.96.0.

## Are there any user-facing changes?

No. This only affects the toolchain used by contributors and CI.

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Dandandan

datafusion/sqllogictest/src/engines/postgres_engine/mod.rs

@@ -75,8 +75,7 @@ impl Postgres {
     ///
     /// See https://docs.rs/tokio-postgres/latest/tokio_postgres/config/struct.Config.html#url for format
     pub async fn connect(relative_path: PathBuf, pb: ProgressBar) -> Result<Self> {
-        let uri = std::env::var("PG_URI")
-            .map_or_else(|_| PG_URI.to_string(), std::convert::identity);
+        let uri = std::env::var("PG_URI").unwrap_or_else(|_| PG_URI.to_string());
 
         info!("Using postgres connection string: {uri}");
 

docs/source/contributor-guide/development_environment.md

@@ -108,7 +108,7 @@ DataFusion is written in Rust and it uses a standard rust toolkit:
 
 - `rustup update stable` DataFusion generally uses the latest stable release of Rust, though it may lag when new Rust toolchains release
   - See which toolchain is currently pinned in the [`rust-toolchain.toml`](https://github.com/apache/datafusion/blob/main/rust-toolchain.toml) file
-  - This can cause issues such as not having the rust-analyzer component installed for the specified toolchain, in which case just install it manually, e.g. `rustup component add --toolchain 1.95.0 rust-analyzer`
+  - This can cause issues such as not having the rust-analyzer component installed for the specified toolchain, in which case just install it manually, e.g. `rustup component add --toolchain 1.96.0 rust-analyzer`
 - `cargo build`
 - `cargo fmt` to format the code
 - etc.

rust-toolchain.toml

@@ -19,5 +19,5 @@
 # to compile this workspace and run CI jobs.
 
 [toolchain]
-channel = "1.95.0"
+channel = "1.96.0"
 components = ["rustfmt", "clippy"]