Closes CosmoStat#713.

The only functional use of sip_tpv in shapepipe was
`split_exp.create_hdus` calling `stp.pv_to_sip(h)` to rewrite each
per-CCD header's TPV distortion keywords as SIP before saving. Modern
astropy (>=5) parses TPV natively via WCSLIB, as do SExtractor, PSFEx,
and every other downstream WCS consumer in the pipeline, so the
keyword-level conversion was no longer buying us anything.

Removing the conversion lets us drop sip_tpv entirely — an unmaintained
2017 package whose v1.1 imports `pkg_resources` at module load and is
incompatible with setuptools>=81 (the underlying cause of the
ModuleNotFoundError in CosmoStat#713; PR CosmoStat#714's setuptools<81 pin is a symptom
workaround).

Changes:
- split_exp: remove sip_tpv import + pv_to_sip call; drop the now-dead
  `transf_coord` plumbing through `process` / `create_hdus`; update
  module docstring accordingly.
- Remove sip_tpv from `depends=[...]` in split_exp_runner,
  python_example_runner, and find_exposures_runner (the last was a
  spurious declaration — find_exposures_package never imported it).
- Drop sip_tpv from environment.yml, environment-dev.yml, Dockerfile,
  install_shapepipe, docs/source/dependencies.md, and the orphan
  shupe:12 BibTeX entry.
- New: `src/shapepipe/tests/test_split_exp.py` — three unittests that
  build a synthetic multi-CCD FITS with TPV distortion, run
  SplitExposures, and verify (1) per-CCD header WCS matches the source
  for several pixel samples, (2) the saved headers .npy round-trips
  pixel→world→pixel, (3) flag output uses int16.

`scripts/jupyter/wcs.ipynb` still imports sip_tpv; it's an exploratory
notebook last touched ~2.5 years ago and left alone.