feat: support PORTAUDIO_ONLY_STATIC envvar for PORTAUDIO_SEARCH_PATH

[hotwatermorning]

PORTAUDIO_SEARCH_PATH と PORTAUDIO_ONLY_STATIC が両方指定されているときは、 PORTAUDIO_SEARCH_PATH で指定されたパスの中から portaudio の static link ライブラリを探索してそれとリンクするようにする

[gemini-code-assist]

Summary of Changes

Hello @hotwatermorning, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

I've implemented a new feature that enhances how the rust-portaudio-sys crate links with the PortAudio library. Specifically, this change allows for static linking of PortAudio when both the PORTAUDIO_SEARCH_PATH and a new PORTAUDIO_ONLY_STATIC environment variable are set. This provides more control over the linking process, enabling users to explicitly opt for static linking from a specified path.

Highlights

• Static Linking Control: I've added logic to build.rs that enables static linking of the PortAudio library. This is activated when both PORTAUDIO_SEARCH_PATH and the newly introduced PORTAUDIO_ONLY_STATIC environment variable are present.
• Static Library Verification: The build script now verifies the existence of the static PortAudio library file within the PORTAUDIO_SEARCH_PATH before attempting to link it, ensuring robustness.
• Platform-Specific Static Library Names: I've introduced PORTAUDIO_STATIC_LIB_NAME constants in platform-specific modules to correctly identify the static library file (e.g., libportaudio.a for Unix-like systems and portaudio.lib for Windows).

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[gemini-code-assist]

Code Review

This pull request adds support for finding and linking a static PortAudio library when PORTAUDIO_SEARCH_PATH and PORTAUDIO_ONLY_STATIC environment variables are set. The changes are generally good, but there's a significant cross-platform issue with path construction that needs to be addressed. I've also pointed out an opportunity to reduce code duplication for better maintainability.

[gemini-code-assist]

Using format! to join path segments is not cross-platform compatible as it assumes a / separator, which will fail on Windows. You should use std::path::Path::join to construct paths robustly. Additionally, path.is_file() is a more direct way to check for a file's existence, and a custom panic! message can be more descriptive than expect. The leading :: on ::std::fs::metadata is also unnecessary.

Suggested change

	let static_lib = format!("{}/{}", search_path, platform::PORTAUDIO_STATIC_LIB_NAME);
	::std::fs::metadata(&static_lib).expect(&format!("{} is not found", static_lib));
	let static_lib_path = std::path::Path::new(&search_path).join(platform::PORTAUDIO_STATIC_LIB_NAME);
	if !static_lib_path.is_file() {
	panic!("Static library not found: {}", static_lib_path.display());
	}

[gemini-code-assist]

To avoid duplicating this constant, you can re-export PORTAUDIO_STATIC_LIB_NAME from the unix_platform module, where it's already defined with the same value.

Suggested change

	pub const PORTAUDIO_STATIC_LIB_NAME: &'static str = "libportaudio.a";
	pub use super::unix_platform::PORTAUDIO_STATIC_LIB_NAME;