fix: add TXE timeout flake pattern to .test_patterns.yml

[AztecBot]

Summary

• Adds a flake pattern for TXE (Test Execution Environment) timeout failures in noir-contracts tests
• These tests fail intermittently with "Timeout waiting for TypeScript callback for contract instance" — an infrastructure issue unrelated to code changes
• Without an owner entry, the CI treats these as hard failures instead of retryable flakes

Failing tests

• public_immutable_contract tests::reading_after_initialization_succeeds (log)
• private_voting_contract test::first::test_end_vote (log)

Both failed with the same TXE timeout error during the merge-train/barretenberg CI run for PR #21392 (C++ ecc test unification — completely unrelated to these Noir contract tests).

Test plan

• YAML syntax validated with yq
• Pattern match verified against both failing test commands
• error_regex matches the TXE timeout error string

ClaudeBox log: https://claudebox.work/s/c97884eeb30213c7?run=1

[AztecBot]

Automatically closing this stale claudebox draft PR (no updates for 5+ days). Re-open if still needed.