chore: upgrade to vitest 5 and migrate benchmarks to vitest bench

[alexvictoor]

Summary

• Bump vitest from ^4.1.4 to ^5.0.5.
• Replace the seven benny-based scripts in src/bench/*.ts with vitest bench files (src/bench/*.bench.ts), sharing a buildFilledHistogram helper in src/bench/support.ts.
• Add an npm run bench script (vitest bench --reporter=verbose) and a benchmark.include entry in vitest.config.ts.
• Remove the benchmark, benny and @types/benchmark dev dependencies (the lockfile shrinks by roughly 1,100 lines).
• Exclude src/bench/** from tsconfig.build.json so bench files stay out of dist.

Notes

• The benchmarks no longer write chart.html reports. Results print to the terminal through the verbose reporter.
• The Histogram add bench no longer has a WASM Packed Histogram case. The other suites keep all of their cases.

Test plan

• npm ci
• npm run tsc
• npm test: 196 passed, 4 skipped
• npm run bench (not run)

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