feat: add magic sccache integration for cmake

[wolfv]

No description provided.

[Copilot]

Pull Request Overview

This PR implements magic integration for sccache with CMake by dynamically detecting its presence via environment variables and adjusting the build requirements accordingly.

• Introduces sccache detection and injects it as a dependency in the CMake configuration
• Propagates the sccache flag in the BuildScriptContext

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
crates/pixi-build-cmake/src/cmake.rs	Adds sccache dependency when an env var with SCCACHE prefix is found
crates/pixi-build-cmake/src/build_script.rs	Adds a new flag "has_sccache" to the build script context

Files not reviewed (1)

• crates/pixi-build-cmake/src/build_script.j2: Language not supported

Comments suppressed due to low confidence (1)

crates/pixi-build-cmake/src/cmake.rs:116

• Using starts_with to detect sccache may inadvertently capture environment variables that merely begin with 'SCCACHE' instead of exactly matching. Consider checking for equality with a specific variable (e.g., key == "SCCACHE") to avoid false positives.

let has_sccache = std::env::vars().any(|(key, _)| key.starts_with("SCCACHE"));