refs: cleanup code around optimizations

This is extracted from a recent series I sent 1, which I've dropped. I think these patches hold value individually.

They mostly cleanup code around 'git refs optimize' which was added recently in db0babf9 (Merge branch 'ms/refs-optimize', 2025-10-02). The code in the refs subsystem contains both 'pack-refs' and 'optimize' functions, which are one and the same.

This series unifies this to only retain the 'optimize' functions and naming, since it backend generic.

This is based on top of master b660e2dc (Sync with 'maint', 2025-10-14) with 'ps/ref-peeled-tags' merged in.

Signed-off-by: Karthik Nayak karthik.188@gmail.com

--- b4-submit-tracking --- { "series": { "revision": 1, "change-id": "20251015-refs-code-cleanup-871a7ce7c8dd", "prefixes": [] } }

Closes: #606