refactor(redis): simplify RedisFactory connection setup and error handling

[joshtrichards]

Summary

Refactor RedisFactory to make connection setup easier to follow and version/configuration errors more actionable.

Changes:

• extract standalone connection setup into a helper
• extract auth argument building into a helper
• centralize Redis/cluster config resolution
• cache Redis capability/version checks
• improve Redis-related exception messages by including detected php-redis version state
• throw \UnexpectedValueException instead of generic \Exception when cluster seeds is missing
• clean up related comments and docblocks
• simplify guard clauses, reduce legacy nesting, enable strict_types

Notes:

• no intended functional change beyond throwing \UnexpectedValueException when the seeds attribute is missing
• cluster configuration still takes precedence over standalone Redis configuration
• ssl_context handling remains unchanged; unsupported versions now produce more informative exception messages

TODO

• Confirm tests pass as-is
• Outside scope of PR itself, but determine if redis.persistent is intentionally (or merely inadvertently) undocumented

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI