v.1.2.7

- Pin pmc to MIT-SPARK fork (windows MSVC compat patches:
  POSIX header guards + std::chrono get_time + std::atomic
  early-exit flag + MSVC-aware compile options).
- Wheel CI: ubuntu-22.04 host (20.04 hosted runners retired),
  fail-fast=false, CIBW_ARCHS=auto64 (xenium needs 64-bit
  pointers). Linux manylinux x86_64 wheel verified green.
- windows-2022 wheel deferred to follow-up PR (ROBIN's own
  src/pkc.cpp uses GCC builtin atomics + size_t OpenMP for
  indices that MSVC OpenMP 2.0 rejects).