fix(ca_utils): harden instance delay and lock error handling

[mkoura]

Lock timeouts and filesystem errors during instance reservation surfaced as raw tracebacks; odd directory or delay-file names could crash parsing or alias to a wrong instance number.

• catch filelock.Timeout and OSError in delay/undelay/create paths, log actionable message, return failure instead of traceback
• require ASCII digits when parsing instance numbers from state-cluster dirs and delay files (isdigit() passes for Unicode digits that int() rejects or maps to a different instance)
• re-touch delay files with future mtime (wall clock stepped back) so the delay window stays bounded; fail closed on touch errors
• treat undelay as best-effort: warn instead of error, stale delay expires within DELAY_VALID_SEC on its own
• document False-return contracts and DELAY_LOCK precondition

[Copilot]

Pull request overview

This PR hardens testnet instance reservation/delay handling by improving lock/filesystem error paths and making instance parsing more robust against unexpected directory or delay-file names.

Changes:

• Wrap instance reservation/delay operations with filelock.Timeout and OSError handling to avoid raw tracebacks and return clean failures.
• Require ASCII digits when parsing instance numbers from state-cluster directories and delay status files, logging warnings for unexpected names.
• Add bounded delay semantics (DELAY_VALID_SEC) and re-touch future-dated delay files to keep the delay window stable when clocks move backwards.

Reviewed changes

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

File	Description
src/cardonnay/cli_create.py	Reserves an instance under DELAY_LOCK, avoids tracebacks on lock/FS failures, and selects the first available non-delayed instance when instance_num < 0.
src/cardonnay/ca_utils.py	Adds DELAY_VALID_SEC, hardens parsing of instance IDs, and improves delay/undelay behavior and documentation around delay-file lifecycle.

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