fix: resolve CI failures from v4 launch

[hyp3rd]

• Change test baseTime from Jan 1 to Jun 3 to prevent januaryFirstOffsetSpec from firing unexpectedly (negative WaitGroup)
• Handle missing go.sum in tidy-check CI steps (no dependencies)
• Increase chain_test timing constants for race-detector stability

[Copilot]

Pull request overview

Addresses CI instability introduced around the v4 launch by making fake-clock tests less date-sensitive, improving go mod tidy checks when no go.sum is present, and relaxing timing constants to reduce race-detector flakiness.

Changes:

• Move fake-clock baseTime from Jan 1 to Jun 3 to avoid month-specific cron specs firing unexpectedly in tests.
• Update CI “tidy check” steps to not hard-fail when go.sum doesn’t exist.
• Increase timing constants in chain-related tests to improve stability under the race detector.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
cron_test.go	Adjusts fixed fake-clock anchor date and updates related test comment to avoid month-specific spec interactions.
chain_test.go	Increases sleep/duration constants to reduce timing flakiness (esp. with -race).
.github/workflows/lint.yml	Tweaks tidy-check diffing to handle absence of go.sum.
.github/workflows/go.yml	Mirrors tidy-check adjustment in the main Go workflow.

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[Copilot]

The test ! -f go.sum || ... guard will skip the diff check when go mod tidy removes a previously-tracked go.sum (file no longer exists), so CI could pass even though the deletion wasn’t committed. Consider guarding on whether go.sum is tracked (e.g., via git ls-files --error-unmatch go.sum) and then always running git diff --exit-code -- go.sum to catch modifications and deletions, while still supporting repos that don’t track go.sum.

Suggested change

	test ! -f go.sum || git diff --exit-code go.sum
	if git ls-files --error-unmatch go.sum >/dev/null 2>&1; then
	git diff --exit-code -- go.sum
	fi

[Copilot]

Same issue as in lint.yml: checking file existence will miss the case where a tracked go.sum gets deleted by go mod tidy (since the file won’t exist and the diff check is skipped). Prefer checking whether go.sum is tracked, then diff it (which will report deletions), while skipping entirely when it’s not tracked in the repo.

Suggested change

	test ! -f go.sum || git diff --exit-code go.sum
	if git ls-files --error-unmatch go.sum >/dev/null 2>&1; then
	git diff --exit-code go.sum
	fi