feat: add support for u-blox enhanced NMEA frames (RMCE and GGAE)

[julienzarka]

Description

This PR adds support for u-blox proprietary enhanced NMEA sentence types RMCE and GGAE. These are vendor-specific extensions of the standard RMC and GGA frames that provide higher precision coordinates.

Changes

• Parser Updates: Modified parse_sentence_type() to support 4-character sentence types (vendor-specific extensions)
• Sentence Types: Added RMCE and GGAE variants to SentenceType enum
• Parsers: Implemented parse_rmce() and parse_ggae() functions that reuse existing RMC/GGA parsing logic (DRY principle)
• Integration: Added enhanced frames to ParseResult enum and parser match statements
• Features: Added RMCE and GGAE features to Cargo.toml under vendor-specific category
• Documentation: Updated README.md with enhanced frame support

Implementation Details

• Enhanced frames use 4-character sentence types (RMCE, GGAE) instead of standard 3-character types
• The parser attempts 4-character types first, then falls back to 3-character types for backward compatibility
• Parsers reuse existing RMC/GGA parsing logic, maintaining code consistency and following DRY principles
• Follows existing patterns similar to other vendor extensions (e.g., RMZ)

Testing

• Added unit tests for both enhanced frame types
• All existing tests pass (91 tests total)
• Tests verify correct parsing of enhanced frames with higher precision coordinates

Breaking Changes

None. This is a backward-compatible addition that extends the crate's capabilities without affecting existing functionality.

Related

Addresses the need for u-blox M10 receiver enhanced frame support in GNSS applications.