Do not lower the process listener limit for small checks

[deepanshupal]

Fixes #405.

calc() called process.setMaxListeners(files + 1). With one input file that sets the limit to 2, below Node's default of 10, so the three SIGINT/SIGTERM listeners that @puppeteer/browsers adds when the time plugin launches Chrome trigger MaxListenersExceededWarning.

The limit now only goes up: it is set only when files + 1 is above the current limit. Multi-file runs behave as before, since scripts/max-listeners-check.sh still passes.

Tests: added test/calc.test.js (the limit stays at 10 for one file, and rises to 21 for 20 files). The first test fails before the change (limit becomes 2) and passes after. Full vitest run passes (26 files, 269 tests) and scripts/max-listeners-check.sh passes.

I could not reproduce the warning end to end with the repo's own time setup, because the Estimo/puppeteer versions in the workspace register fewer listeners than in the report. To check the cause I called calc() for one file and then added three SIGINT and three SIGTERM listeners, like @puppeteer/browsers does: 2 warnings before the change, 0 after.

AI-assisted: written with Claude, and I ran the tests above myself.

[ai]

Thanks.

Do you need a release of this feature soon or we can release it with bigger changes?

[deepanshupal]

No rush at all - happy for it to ride with the bigger release. Thanks for the quick merge!

[ai]

Released in 14.2.0.