refactor: disable pnp when bench

[stormslowly]

Note: it's not a perf PR.
It simply disables PnP features in the file system while performing non-PnP-related benchmarks, and separates performance concerns.

[codspeed-hq]

CodSpeed Performance Report

Merging #134 will improve performances by 57.52%

_{Comparing chore/filesytem_opts (cfbf58f) with main (8238fcf)}

Summary

⚡ 3 improvements
✅ 3 untouched

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	resolver[multi-thread]	95.9 ms	74 ms	+29.49%
⚡	resolver[resolve from symlinks]	359.5 ms	228.2 ms	+57.52%
⚡	resolver[single-thread]	89.3 ms	63.4 ms	+40.79%

[Copilot]

Pull request overview

This PR refactors the benchmark code to properly disable Plug'n'Play (PnP) features during non-PnP-related benchmarks, separating performance concerns. The changes introduce a new FileSystemOptions struct to control PnP behavior and update benchmarks to explicitly set PnP flags.

Key changes:

• Added FileSystemOptions struct with enable_pnp field to configure filesystem behavior
• Introduced FileSystemOs::new() constructor to accept custom filesystem options
• Updated benchmark resolver creation to explicitly disable PnP for non-PnP benchmarks

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/lib.rs	Exports FileSystemOptions to make it available for benchmarks
src/file_system.rs	Adds FileSystemOs::new() method to accept custom options
benches/resolver.rs	Refactors resolver creation to accept PnP flag and disables it for non-PnP benchmarks

---

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[Copilot]

The enable_pnp parameter is only used when the yarn_pnp feature is enabled. To avoid compilation warnings about unused parameters when the feature is disabled, consider either:

1. Prefixing the parameter with an underscore: _enable_pnp: bool
2. Or applying a #[allow(unused_variables)] attribute when the feature is disabled

Example:

fn rspack_resolver(
  #[cfg_attr(not(feature = "yarn_pnp"), allow(unused_variables))]
  enable_pnp: bool
) -> rspack_resolver::Resolver {

Suggested change

	fn rspack_resolver(enable_pnp: bool) -> rspack_resolver::Resolver {
	fn rspack_resolver(
	#[cfg_attr(not(feature = "yarn_pnp"), allow(unused_variables))]
	enable_pnp: bool
	) -> rspack_resolver::Resolver {