perf(parser): mark error paths as cold

[DonIsaac]

What This PR Does

Adds #[cold] to parser functions that record errors.

I'm making a draft for now to run benchmarks and see if my hypothesis is correct. Locally I saw some improvement, but my machine gets finicky when it heats up, so it could be noise.

Hypothesis

LLVM will consider call sites of cold functions to also be cold (assuming that the function is always called). By marking error recording functions as #[cold], if statements that check for diagnostics should be considered cold themselves, thus hinting to branch predictors that the happy path is more likely. This should give branch prediction a higher success rate and lower the odds the CPU's pipeline gets thrown out.

e.g.

fn parse_foo(&self) -> FooNode {
  if some_bad_thing {
    // this block post-dominates call to `error`, suggesting that it won't be called
    // frequently
    self.error(diagnostics::bad_thing_happened());
  }
  // happy path continues
}

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[Boshen]

I tried in #10599, but I think it makes sense to merge this change.

I just recalled codspeed doesn't weigh in branch predictions, so we need to rely on wall clock benchmark + cpu instrustions.

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #10614 will not alter performance

_{Comparing DonIsaac:don/parser/perf/cold-errors (7f18ca4) with main (fae8c26)}

Summary

✅ 36 untouched benchmarks