* fix(redis): handle float redis_version from AWS ElastiCache Valkey
AWS ElastiCache Valkey returns redis_version as a float (7.0) instead
of a string ('7.0.0'), causing AttributeError: 'float' object has no
attribute 'split' in async_lpop when parsing version for LPOP count.
Changes:
- Extract version parsing into _parse_redis_major_version() helper
- Add DEFAULT_REDIS_MAJOR_VERSION constant (replaces magic number)
- Support multiple version formats: string, float, int, malformed
- Add comprehensive test coverage for all version format edge cases
Fixes: 'LiteLLM Redis Cache LPOP: - Got exception from REDIS' error
during db_spend_update_job cronjobs
* refactor: move DEFAULT_REDIS_MAJOR_VERSION to constants.py
727fe504bb