fix: deduplicate installer functions and harden backup/restore flows

[yuanyp8]

Motivation

• Remove duplicated function definitions to eliminate override ambiguity and improve maintainability.
• Prevent backup/restore/verify flows from failing silently due to implicit root-password fallback and improve UX for external MySQL targets.
• Make restore/snapshot selection and NFS backup behavior more robust when files/permissions are missing.
• Improve benchmark observability and avoid unstable log-following behavior.

Description

• Deduplicated and consolidated implementations in install.sh (kept single active definitions for parsing, auth preparation, backup/restore/benchmark flows and helper functions), and added --registry and --nodeport-enabled parameters with NODEPORT_ENABLED flag and optional NodePort manifest block rendering in manifests/innodb-mysql.yaml.
• Hardened auth handling so backup|restore|verify-backup-restore now require an explicit --mysql-password or --mysql-auth-secret, updated prepare_runtime_auth_secret to fail fast for those actions, and added precheck_mysql_connectivity() which validates MySQL connectivity before launching backup/restore/verify jobs (calls added to run_backup, run_restore, verify_backup_restore).
• Made restore snapshot resolution resilient: when latest.txt points to a missing snapshot the code falls back to the newest existing *.sql.gz, and added an NFS write test (touch) during backup to fail early if snapshot directory is not writable; these changes are in manifests/mysql-backup-support.yaml.
• Improved benchmark logic by changing prepare-buffer calculation to ceiling division with a reasonable lower bound, replacing repeated kubectl logs -f followers with periodic kubectl logs --tail=10 polling to avoid multiple background followers, and emitting a JSON report (in addition to text) plus MySQL-8 specific compat args in manifests/mysql-benchmark-job.yaml.

Testing

• Ran bash -n install.sh to validate shell syntax and it returned no errors (success).
• Verified duplicate-function removal with an awk scan that shows no remaining duplicated name() { ... } definitions in install.sh (success).
• Committed changes and updated affected manifests: install.sh, manifests/innodb-mysql.yaml, manifests/mysql-backup-support.yaml, and manifests/mysql-benchmark-job.yaml.

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Codex Task