fix(swc): do not inherit watch mode when transpiling newly added files

[higuaifan]

PR Checklist

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• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Other... Please describe:

What is the current behavior?

The "transpile newly added file" callback in the swc builder re-invokes swcCli.default() with watch: true inherited from the outer options. Per added file (renames and git checkouts count — atomic writes surface as add), this registers one more permanent chokidar watcher inside @swc/cli (stacked watchers → duplicate compiles and back-to-back restarts) and constructs one more Piscina worker pool that @swc/cli never destroys (swc-project/pkgs#126) — a week-long watch session accumulated ~1,700 idle worker threads / ~15 GB.

Issue Number: #3482

What is the new behavior?

The added-file invocation is one-shot: watch: false stops the watcher stacking, and sync: true skips spawning a worker pool to transpile a single file. Unit test added.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

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This PR — investigation, patch, test, and local CI verification — was engineered by Claude; I'm following up and available for changes if wanted.