Fix WithRedactionKeys validation inconsistency

[Copilot]

The WithRedactionKeys validation exhibited inconsistent behavior: passing all-whitespace keys would fail if no default keys existed, but succeed if default keys were present. This created unpredictable behavior based on initialization state.

Changes

• Track addedCount of normalized keys actually added, validate against this instead of total key count
• Update documentation to reflect consistent validation behavior regardless of existing keys

Example

// Previously: succeeds because default keys exist in cfg.keys
r, err := NewRedactor(WithRedactionKeys("   ", "\t", "\n"))

// Now: consistently fails since no valid keys were added
r, err := NewRedactor(WithRedactionKeys("   ", "\t", "\n"))
// err == ErrInvalidRedactorConfig

Test coverage added for edge cases: all-whitespace keys, mixed valid/invalid keys.

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[Copilot]

Pull request overview

This PR fixes a validation inconsistency in WithRedactionKeys where all-whitespace keys would fail validation only when no default keys existed, but succeed when default keys were present. The fix tracks the count of valid keys actually added from the input and validates against this count, ensuring consistent behavior regardless of the initialization state.

Changes:

• Modified WithRedactionKeys to track addedCount of normalized keys that were actually added, validating against this instead of the total keys in the configuration
• Updated documentation to clarify that validation is consistent regardless of existing keys
• Added comprehensive test coverage for edge cases including all-whitespace keys, empty keys, valid keys, and mixed valid/invalid keys

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
pkg/secrets/redact.go	Fixed validation logic to use addedCount instead of len(cfg.keys) and updated documentation to reflect consistent validation behavior
pkg/secrets/secrets_test.go	Added TestWithRedactionKeysValidation with comprehensive test cases for the validation edge cases

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