Fix: Improve RFC3339 date parsing validation (Issue #2418)

[Naman-cell]

• Replace search() with fullmatch() for strict RFC3339 format validation
• Provide clear, actionable error messages with expected format
• Add input whitespace stripping before validation
• Improve exception handling with specific ValueError messages
• Add comprehensive test cases for invalid formats

Test: Existing tests pass + new test cases added

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