fix(quickadapter): prefix `compose_sample_weights` and `sanitize_and_renormalize...

fix(quickadapter): prefix `compose_sample_weights` and `sanitize_and_renormalize` log entries with caller context (#97)

`compose_sample_weights` and `sanitize_and_renormalize` accept a
required keyword-only `context: str` parameter; every warning, error,
and inner `sanitize_and_renormalize` call uses `context` as its sole
prefix.

- `compose_sample_weights(..., *, logger, context, on_collapse=...)`:
  `context: str` keyword-only, required. The 4 internal
  warnings/errors (shape-mismatch `ValueError`, all-dropped
  `LabelWeightSupportError`, sparse-mass warning, collapse-on-
  survivors `LabelWeightSupportError` and fallback warning) prefix
  with `{context}:`. Internal `sanitize_and_renormalize` calls
  compose sub-contexts: `{context}:base_only`,
  `{context}:label_weighted`, `{context}:base_fallback`. The sparse-
  mass message reads `sparse weighting mass`, accurate for both
  train and eval paths.
- `sanitize_and_renormalize(..., *, logger=None, context: str)`:
  `context` keyword-only, required. The 5 warnings/errors
  (`drop_mask` shape `ValueError`, `drop_mask` dtype `ValueError`,
  rescale-overflow warning, weights-collapsed warning,
  mask-covers-all warning) prefix with `{context}:`. The redundant
  `(context=%s, ...)` subfield is dropped.
- 5 `compose_sample_weights` call sites in
  `QuickAdapterRegressorV3.py` pass `context=context`. The 2
  external `sanitize_and_renormalize` call sites
  (`post_feature_pipeline:train`, `post_feature_pipeline:test`)
  already pass `context=`.

Log format goes from
`compose_sample_weights: sparse training mass (59/2603 rows ...)`
to
`[ETH/USDT] train_test_split:train: sparse weighting mass (59/2603 rows ...)`.
The pair, split method, and train/eval side are traceable in the
log line.