Handle tsc watch and profiling signals

[Jake Bailey (jakebailey)]

Fixes #63856

[Copilot]

Pull request overview

Fixes unresponsive tsc interruption by scoping signal handling to watch mode and preserving profiling output during termination.

Changes:

• Adds reusable termination-signal utilities.
• Flushes profiles before re-raising termination signals.
• Configures watch-specific cancellation and adds Unix profiling coverage.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tsc/cmd/tsc/main.go	Configures watch signal handling.
tsc/internal/execute/tsc.go	Applies signal contexts to unprofiled watch modes.
tsc/internal/osutil/osutil.go	Adds termination notification helpers.
tsc/internal/osutil/signal_unix.go	Re-raises Unix signals.
tsc/internal/osutil/signal_other.go	Provides the non-Unix fallback.
tsc/internal/pprof/pprof.go	Flushes profiles safely upon termination.
tsc/internal/pprof/pprof_unix_test.go	Tests profile flushing on SIGINT.

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