bench: move to dev-dependencies

[AsakuraMizu]

Move criterion and rand to dev-dependencies.

Now the bench feature is useless and deprecated. Or we can remove it now.

[Copilot]

Pull request overview

Moves benchmark-only crates out of the main dependency graph by relocating criterion and rand to dev-dependencies, and updates docs/bench configuration so cargo bench no longer needs a bench feature.

Changes:

• Move criterion and rand from optional [dependencies] to [dev-dependencies] and deprecate the bench feature (now a no-op).
• Remove required-features = ["bench"] from all [[bench]] targets so benchmarks run by default.
• Update top-level README benchmark commands to drop --features bench.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
Cargo.toml	Shifts benchmark deps to dev-dependencies, deprecates bench feature, and makes benches runnable without feature gates.
benches/README_CN.md	Updates benchmark commands to stop requiring --features bench (but still has a couple leftover references to bench).
README.md	Updates benchmark command to cargo bench (but references a non-existent benches/README.md).
README_CN.md	Updates benchmark command to cargo bench.

Comments suppressed due to low confidence (3)

benches/README_CN.md:17

• The prerequisites text above this command still says benchmarks require enabling the bench feature to pull in criterion/rand, but those dependencies are now dev-dependencies and cargo bench works without --features bench. Please update the prerequisites section to match the new Cargo.toml behavior.

rustup install 1.93.0

# 使用指定版本运行 benchmark
cargo +1.93.0 bench

**README.md:163**
* `benches/README.md` is referenced here, but there is no `benches/README.md` file in the repository (only `benches/README_CN.md`). This link will mislead users; either add the English README under `benches/README.md` or update the reference to an existing document.

cargo bench

For detailed usage instructions, refer to `benches/README.md`.

benches/README_CN.md:59

• This section still implies benchmarks need the bench feature and also uses --features "bench tracking", but bench is now deprecated/no-op and benchmarks should run without it. Update the wording and the command to use only --features tracking (and remove references to enabling bench).

# 启用 memory tracking 功能运行 benchmark
cargo +1.93.0 bench --features "bench tracking"

# 保存基线用于后续对比
cargo +1.93.0 bench -- --save-baseline main

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