Retry attempt InstantDDL up to --default-retries

[meiji163]

Following on #1651, increase the max instant DDL attempts from 5 to MaxRetries, which is configurable with --default-retries. In high-concurrency environments, we may need more retries due to metadata lock wait timeout.

In case this PR introduced Go code changes:

• contributed code is using same conventions as original code
• script/cibuild returns with no formatting errors, build errors or unit test errors.

[Copilot]

Pull request overview

This PR updates the instant DDL retry behavior to use the configurable --default-retries value (via MigrationContext.MaxRetries()) instead of a hard-coded retry limit, to better tolerate lock wait timeouts in high-concurrency environments.

Changes:

• Pass MigrationContext.MaxRetries() into the instant DDL lock-wait retry helper.
• Update retryOnLockWaitTimeout to accept a configurable maxRetries and iterate using int64.

Show a summary per file

File	Description
go/logic/applier.go	Make instant DDL lock-wait retries configurable via MaxRetries() and adjust retry helper signature/loop accordingly.

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Comments suppressed due to low confidence (1)

go/logic/applier.go:323

• maxRetries now comes from MigrationContext.MaxRetries() (default 60 and user-configurable to arbitrarily large values). With the current linear backoff (i * 5s) this can make an instant DDL attempt block the migration start for hours by default, and for large --default-retries values it can overflow time.Duration (overflow occurs once i > ~1.8e9), potentially producing negative/short sleeps and a tight retry loop. Consider capping maxRetries for this helper and/or capping the sleep interval (or switching to a bounded exponential backoff) and defensively handling very large values.

func retryOnLockWaitTimeout(operation func() error, maxRetries int64, logger base.Logger) error {
	var err error
	for i := int64(0); i < maxRetries; i++ {
		if i != 0 {
			logger.Infof("Retrying after lock wait timeout (attempt %d/%d)", i+1, maxRetries)
			RetrySleepFn(time.Duration(i) * 5 * time.Second)
		}

• Files reviewed: 2/2 changed files
• Comments generated: 1