Extract build polling and share between bk build watch and bk preflight

[matthewborden]

This extracts the build polling loop from bk build watch into a shared internal/build/watch package and reuses it in bk preflight.

Previously bk build watch had its own inline polling loop with no error tolerance, and bk preflight would create the build and exit immediately. With this change:

• bk preflight now watches the build until completion by default (--no-watch to disable)
• Both commands share the same polling logic with retry tolerance (10 consecutive API errors before aborting) and per-request timeouts
• The preflight summary covers all job states:

Summary	Job States
passed	passed
failed	failed, timed_out
canceled	canceled
running	running, canceling, timing_out
scheduled	scheduled, assigned, accepted, reserved
blocked	blocked, blocked_failed
skipped	skipped, broken
waiting	waiting, waiting_failed, pending, limited, limiting, platform_limited, platform_limiting, expired

Unknown states, and non-command jobs are ignored.

Verification

1. Run bk build watch -p <pipeline> and confirm it behaves as before.
2. Run bk preflight -p <pipeline> and confirm it polls and prints job state updates until the build finishes.
3. Run bk preflight -p <pipeline> --no-watch and confirm it exits after creating the build.
4. mise run test