perf(plugin-pnp): only reload pnpapi when it changes

[merceyz]

What's the problem this PR addresses?

The cache introduced in #2564 only survives as long as the linker instance does, this means it doesn't affect running multiple scripts (i.e. postinstalls) since new linkers are created every time.

How did you fix it?

A dynamicRequireFresh (naming suggestions welcome) function that caches the module globally and only reloads it if the file changed

Result

Tested on the gatsby benchmark

berry/scripts/bench-run.sh

Lines 74 to 76 in 5411f76

	bench install-cache-and-lock \
	--prepare 'rm -rf .yarn .pnp.*' \
	'yarn install'

$ YARN_IGNORE_PATH=1 hyperfine -w 5 --prepare="rm -rf .yarn" 'node before.cjs' 'node after.cjs'
Benchmark #1: node before.cjs
  Time (mean ± σ):      8.931 s ±  0.194 s    [User: 11.532 s, System: 4.739 s]
  Range (min … max):    8.760 s …  9.325 s    10 runs

Benchmark #2: node after.cjs
  Time (mean ± σ):      8.290 s ±  0.072 s    [User: 10.918 s, System: 4.517 s]
  Range (min … max):    8.216 s …  8.457 s    10 runs

Summary
  'node after.cjs' ran
    1.08 ± 0.03 times faster than 'node before.cjs'

Checklist

• I have read the Contributing Guide.
• I have set the packages that need to be released for my changes to be effective.
• I will check that all automated PR checks pass before the PR gets reviewed.

[arcanis]

I read "fresh" as implying the require is always up-to-date. Perhaps instead the public API could be:

type RequireCache = 'mtime' | null;

export function dynamicRequire(path: PortablePath, opts: {cache: RequireCache}) {

Also, perhaps dynamicRequireNoCache should burst the entry in dynamicRequireFreshCache?