perf: speed up config loading

[Cherry]

Speeds up config loading at startup without changing behaviour, brings dependencies up to date, and fixes a flaky test.

• Skip a redundant clone: loadConfig no longer runs _.cloneDeep before _.merge on JSON config files. _.merge already copies plain objects and arrays, so the clone did nothing.
• Parse JSON first: the JSON handler now tries JSON.parse first and only strips comments if that fails. Most config files containing // are just URLs, not comments.
• Dependencies:
  • nanoid 5 → 6. Same output; random() already guards against the sizes that now throw.
  • vitest and coverage 4 → 5.
  • Raised the minimum versions for dayjs and lodash.
  • Removed the poolOptions block from the vitest config, which vitest has ignored since v4.
• Flaky test: "allows the process to exit gracefully" sometimes timed out on macOS. The test harness treated the child as finished on exit, which can fire before its output has been fully read. It now waits for close, and the test checks the full output instead of individual chunks.

Results

setup() time, excluding autoload, median of 15 runs on three production app configs:

Config size	Before	After
Large (~200 config files)	82ms	73ms (−11%)
Medium (~45 config files)	34ms	30ms (−11%)
Small (~35 config files)	25ms	23ms (−8%)

Testing

• The resulting config and codes are identical to before for all three apps.
• Ran every config file from those apps, plus edge cases, through the old and new JSON handler. Results and error messages match.
• Added regression tests for // and /* inside JSON strings, config not sharing objects with cached JSON, and code() with null or frozen data.
• Reproduced the macOS flake by delaying stdout until after exit: the old test fails with the same timeout seen in CI, and the fixed one passes.