sloproxy

feat(auth): introduce weighted round-robin scheduler and credential weight validation master

- Added support for weighted round-robin authentication scheduling strategy. - Implemented credential weight validation for attributes and metadata, with strict error handling for invalid weights. - Enhanced scheduler with smooth weighted state handling and proportional selection logic. - Introduced tests for credential weight parsing, validation, and weighted round-robin behavior. - Updated configuration to include `weight` field for credentials with range validation. Closes: #4470