build: cache compiler outputs with ccache

[jaagut]

Summary

Enable ccache for C and C++ workspace builds and persist compiler outputs in the benchmark workflow.

Proposed changes

• Add ccache to the shared ROS Pixi feature so it is present in both default and robot environments.
• Configure CMake's C and C++ compiler launchers to use ccache.
• Cache ccache data independently per runner OS, architecture, and lockfile.
• Print compiler cache statistics in the benchmark workflow.
• Regenerate pixi.lock for both supported architectures and environments.

Impact

Repeated builds can reuse compiler output without changing the generated program. The first cold build remains representative, while subsequent CI runs and the touched-source incremental build can report cache hits.

Stack

This PR is based on agent/build-benchmark-ninja.

Validation

• Located ccache in the configured Conda channels.
• Installed and ran the locked ccache version in the default Pixi environment.
• Built bitbots_head_mover successfully through the Ninja and ccache launchers.
• Confirmed ccache recorded compiler calls.
• Parsed pixi.toml and ran git diff --check.

[Flova]

While faster build times would be nice I am worried about the hidden state it introduces and that a clean build for example might fail even if the ci on a pull request passed.