#9034 Fix Windows rewatch CI flakes from files opened without delete sharing

Unix.openfile opens files on Windows without FILE_SHARE_DELETE unless asked, so while the watcher read lib/watch.lock (every 100 ms) or hashed a source, other processes could not delete or rename it. Removing the lock then failed with "Device or resource busy" and the watcher kept running; Rust's File::open shares delete by default.

A single failed rm left the watcher running into later tests, where the runner later killed it as an orphan. Retry for five seconds, and kill the watcher when it still does not exit so the failure stays in its test.

The retained-parse test now prints watch.log and calls.log when the edit of B does not re-parse A. A watchdog in the parity step reports and stops runaway rescript/bsc processes: four Windows runners lost contact with GitHub during that step, past its timeout, without any log.

Parallel domains appended to REWATCH_COMPILER_CALL_LOG through separate handles, and Windows emulates append as seek-then-write, so one domain's line could overwrite another's. The retained-parse test then missed A's parse line (and the initial build's implementation line for A) although A was parsed: the Windows "flake" in that test was a lost log line.