[rvitaliy]

Fixes #1006.

Accept options.signal, preserve it in generated request details, and forward it to the native HTTPS request and the per-request proxy agent. Forwarding it to the proxy agent also cancels a pending CONNECT handshake.

Cancellation uses Node.js's native AbortError; socket timeouts and HTTP errors retain their behavior. Custom agents remain responsible for their own connection setup. No new dependencies.

Validation on Node 22.23.4 and 26.13.0: 142 tests passed on each, including 11 new tests for cancellation, signal propagation, cleanup, success, HTTP errors, timeouts, and a stalled proxy. With the original implementation, 10 of the 11 new tests fail; the no-signal compatibility test already passes. Lint passes.

Commands:

npm run lint
npm exec -- c8 --reporter=lcov --reporter=text mocha --ui tdd --ignore test/testBrowsers.js 'test/test*'

Browser tests that deliver notifications through external push providers were not run.