ci: make ccache effective and observable, shallow checkout, add cache…

[MrLi000001]

… warmer

Measured on the self-hosted runners, the Build step of the same workflow ranges from 2.7 min (warm ccache) to 37.5 min (stale ccache), and a full-history checkout took ~12 min on cache-cold runners.

• Set ccache --max-size=30G (default ~10G is tight for -O3 -g builds) and print ccache -s before/after the build so hit rates are visible in every run log (if: always()).
• fetch-depth: 0 -> 1; CMake only runs 'git log -1' for commit info.
• Add cache_warmer.yml: on every push to develop, build (without tests) on both the X64 and gpu pools so /tmp/ccache stays primed with the latest develop. This prevents the first PR runs after a big refactor merge from all paying a full rebuild.

Reminder

• I have read AGENTS.md and docs/developers_guide/agent_governance.md.
• I have linked an issue or explained why this PR does not need one.
• I have added adequate unit tests and/or case tests, or explained why not.
• I have listed the exact verification commands run and their results.
• I have described user-visible behavior changes, including INPUT parameter changes.
• I have explained core-module impact for ESolver, HSolver, ElecState, Hamilt, Operator, Psi, or other source/ changes.
• I have requested any needed governance exception below.

Linked Issue

Fix #

Unit Tests and/or Case Tests for my changes

• Commands run:
• Result summary:
• Checks not run, with reason:

What's changed?

• Example: brief summary of the user-visible or developer-facing change.

Governance Notes

• INPUT/docs changes:
• Core module impact:
• Exceptions requested:

[Stardust0831]

The shallow checkout and ccache statistics are useful, but I suggest splitting out the cache warmer. It is not yet clear whether /tmp/ccache persists across jobs and nodes in the dynamic runner pool, so one warmer may only warm a single node while consuming an additional GPU. It also builds the default seven CUDA architectures, while #7753 uses sm_70, so those CUDA cache entries will not be effectively reused.