v0.2.10 — Batch panchanga primitive + faster tests

Added

• py_compute_panchanga_at_jds(jds) — batch primitive that computes tithi/nakshatra/yoga/karana at many arbitrary instants in a single FFI round-trip. Benchmarks: 8760 JDs in ~1.1s, vs ~45s for a per-JD loop. Designed for muhurat engines (vivah, etc.) that sample panchanga hourly across a year.
• panchang.core.panchang.compute_panchanga_at_jds(jds) — Python wrapper for ergonomic use.

Improved

• Test suite runs in ~70s instead of ~290s (4× faster) via session-scoped fixtures for expensive year-long computations (festivals, batch, ekadashis). No coverage loss.

Compatibility

• Additive — no behavior changes to existing APIs.
• Recommended for downstream packages doing fine-grained panchanga sampling.