entproto: Add proto3 optional label support

[tbxark]

proto3 supports using optional fields to define optional fields, so google/protobuf/wrappers.proto does not need to be used. This will make the generated code more concise.

The EnableOptionLabel can enable this feature for a specific Message individually.

// EnableOptionalLabel enables the optional label in the generated protobuf message instead of google/protobuf/wrappers.proto
func EnableOptionalLabel() MessageOption {
	return func(msg *message) {
		msg.EnableOptionalLabel = true
	}
}

[Copilot]

Pull Request Overview

This PR adds support for proto3 optional field labels as an alternative to using google/protobuf/wrappers.proto for optional fields, resulting in more concise generated code.

• Introduces EnableOptionalLabel() MessageOption to enable proto3 optional labels per message
• Updates field descriptor generation to use proto3 optional labels when enabled
• Maintains backward compatibility by keeping the feature opt-in

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
entproto/message.go	Adds EnableOptionalLabel() MessageOption and corresponding struct field
entproto/adapter.go	Implements optional label logic in field descriptor generation, adds optionalFieldLabel constant, and updates function signatures
entproto/service.go	Updates function call to match new toProtoFieldDescriptor signature

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[Copilot]

Corrected 'repeat' to 'repeated' for grammatical accuracy.

Suggested change

	return extractJSONDetails(f) // repeat fields are not required for optional label.
	return extractJSONDetails(f) // repeated fields are not required for optional label.

[Copilot]

The comment is unclear about why the enableOptionalLabel parameter is not passed to extractJSONDetails. Consider clarifying: 'JSON fields only support repeated (array) types, not optional labels.' This better explains that extractJSONDetails doesn't need the enableOptionalLabel parameter because it only handles repeated fields.

Suggested change

	return extractJSONDetails(f) // repeat fields are not required for optional label.
	return extractJSONDetails(f) // JSON fields only support repeated (array) types, not optional labels.