feat: protobuf edition 2023 support

[abarke]

🚀 Protobuf Edition 2023 Support

✨ Major Features

🎯 Edition 2023 Compatibility

• Partial support for protobuf edition = "2023" syntax
• Feature-based behaviour resolution (vs syntax-based checks)
• Advanced field presence semantics (explicit, implicit, legacy_required)
• Enhanced enum handling (open/closed semantics)

🔧 Infrastructure Updates

• C++ Standard: Upgraded from v14 to v17 📈
• Protobuf Version: Updated from v25.8 to v32.1 📦

📚 New Documentation & Examples

• Requirements for supporting EDITIONS.md
• New Edition 2023 example
• Updated README with editions syntax documentation

⚙️ Code Generation Improvements

• New feature resolution system in prost-build
• Enhanced field presence handling for all protobuf versions
• Improved conformance test support for editions

🧪 Testing & Validation

• Conformance tests pass for edition 2023 (though missing some features)
• Updated failing_tests.txt

⛓️‍💥 Breaking Changes

• Various changes due to upstream proto files caused by protobuf upgrade e.g api.proto
• See semver CI results for more breaking changes (some may be false positives I believe)

🗺️ Missing Protobuf Features

New tests were added to conformance/failed_tests.txt

• Unknown Fields Support for Unknown Fields (Rebase of #574) #1340
• Unknown Ordering (since protobuf v27)
• Delimited encoding/MessageSet (old proto2 extension)

Fixes #1031

[mmmtastymmm]

Yeah! Unknown field support! 🎉

[alebar42]

Yeah! Unknown field support! 🎉

Not in this PR, but this is covered in #1340

Perhaps that should be merged first so I can rebase this branch

[mmmtastymmm]

Yeah! Unknown field support! 🎉

Not in this PR, but this is covered in #1340

Perhaps that should be merged first so I can rebase this branch

My b, commented on the wrong one!