refactor: extract AnophelesHetAnalysis into anoph/heterozygosity.py

- Move heterozygosity and ROH analysis methods from anopheles.py to
  new AnophelesHetAnalysis class in anoph/heterozygosity.py
- Implement _roh_hmm_cache_name property (fixes #900)
- Add ValueError guard for window_size > available sites in _sample_count_het
- Replace deprecated inplace=True in _roh_hmm_predict
- Add unit tests in tests/anoph/test_heterozygosity.py
Part of #366

Author: 31puneet

malariagen_data/anopheles.py

@@ -19,7 +19,6 @@
     dash_params,
     gplt_params,
     hapnet_params,
-    het_params,
     ihs_params,
     plotly_params,
     xpehh_params,
@@ -49,10 +48,9 @@
 from .anoph.heterozygosity import AnophelesHetAnalysis
 from .util import (
     CacheMiss,
-    Region,
+    Region,  # noqa: F401 (re-exported via __init__.py)
     _check_types,
     _jackknife_ci,
-    _parse_single_region,
     _plotly_discrete_legend,
 )