Summary

This PR addresses the same flaky debugger startup race as #61773.

On some macOS CI runs, waitForInitialBreak() can time out even after Debugger attached. and the debug> prompt are observed.
For tests that use waitForInitialBreak() only for startup synchronization (and do not assert initial pause/breakInfo semantics), this PR switches startup sync to attach/prompt-based waiting while keeping test intent unchanged.

• test/parallel/test-debugger-watch-validation.js
  • failed CI log: https://github.com/nodejs/node/actions/runs/21772762644/job/62823422649
• test/parallel/test-debugger-extract-function-name.mjs
  • failed CI log: https://github.com/nodejs/node/actions/runs/22266947520
• test/parallel/test-debugger-random-port-with-inspect-port.js
  • failed CI log: https://github.com/nodejs/node/actions/runs/21785139333/job/62855280668

Testing

UNUSUAL="$HOME/dir with \$unusual\"chars?'åß∂ƒ©∆¬…\`"
mkdir -p "$UNUSUAL"
ln -sfn "$PWD" "$UNUSUAL/node"
cd "$UNUSUAL/node"

• ./tools/test.py -p actions parallel/test-debugger-watch-validation (passes locally)
• ./tools/test.py -p actions parallel/test-debugger-random-port-with-inspect-port (passes locally)
• ./tools/test.py -p actions parallel/test-debugger-extract-function-name (passes locally)
• Additional unusual-path stress runs were executed on this PR branch:
  • ./tools/test.py -p actions -j1 --repeat 50 parallel/test-debugger-watch-validation parallel/test-debugger-random-port-with-inspect-port parallel/test-debugger-extract-function-name
  • ./tools/test.py -p actions -j4 --repeat 100 parallel/test-debugger-watch-validation parallel/test-debugger-random-port-with-inspect-port parallel/test-debugger-extract-function-name
• CI passes on macOS

Refs: #61762