feat: support building protoc from source

[fmorency]

This pull request adds support for building the protoc binary from source as an optional feature, improving build portability and flexibility. The main changes include introducing the protobuf-src dependency and a new build-protoc feature, along with conditional logic in build.rs to use the built protoc binary when the feature is enabled.

Dependency and feature additions:

• Added protobuf-src as an optional dependency in Cargo.toml to allow building protoc from source.
• Introduced the build-protoc feature in Cargo.toml, which enables building protoc from source rather than relying on a system installation.

Build script enhancements:

• Updated build.rs to check for the build-protoc feature and set the PROTOC environment variable to the path of the built protoc binary if enabled, improving build flexibility across different environments.

[Copilot]

Pull Request Overview

This PR adds support for building the protoc binary from source as an optional feature, enhancing build portability by reducing dependency on system-installed protoc.

• Introduces protobuf-src as an optional dependency with a new build-protoc feature
• Updates build script to conditionally use built protoc binary when feature is enabled
• Adds build-time logging to indicate when the feature is active

Reviewed Changes

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

File	Description
Cargo.toml	Adds optional protobuf-src dependency and build-protoc feature
build.rs	Implements conditional logic to use built protoc when feature is enabled

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[Copilot]

Debug print statements should use cargo:warning= prefix for build script output to properly integrate with Cargo's output formatting, or be removed entirely for production builds.

Suggested change

	println!("build-protoc feature is enabled");
	println!("cargo:warning=build-protoc feature is enabled");

[Copilot]

Missing error handling for protobuf_src::protoc(). If the protoc build fails, this will panic at runtime. Consider wrapping in a Result and providing a meaningful error message.

Suggested change

	env::set_var("PROTOC", protobuf_src::protoc());
	let protoc_path = protobuf_src::protoc().map_err(|e| {
	std::io::Error::new(
	std::io::ErrorKind::Other,
	format!("Failed to build protoc: {}", e),
	)
	})?;
	env::set_var("PROTOC", protoc_path);