fix(quickadapter): route reversed train weights through support_policy (#98)

fix(quickadapter): route reversed train weights through support_policy (#98)

PR #85 added `_compose_train_weights_with_support` (gates training-set weights through `support_policy`) and `_compose_eval_weights` (eval-side, deliberately bypasses `support_policy`). The `reverse_train_test_order` path in `_make_train_test_split_datasets` and `_make_timeseries_split_datasets` swapped slices AT THE FINAL `build_data_dictionary` call -- AFTER weight composition -- so the actual-train slot received weights composed by `_compose_eval_weights` (silent bypass), and the actual-test slot received weights composed by `_compose_train_weights_with_support` (wrong direction, typically a no-op under `support_policy='fallback'` default).

Reachable only under `causal_mode=false` (deprecated; acausal baselines only) since `causal_mode=true` rejects `reverse_train_test_order=true` upfront.

Fix: perform the train/test slice swap BEFORE weight composition so the `train_*` and `test_*` identifiers map to their actual training roles throughout. Both call sites converge to a single `dk.build_data_dictionary` return; context strings in `support_policy` log/raise messages now reflect the true train/test role.

Add an upfront `ValueError` in `_make_train_test_split_datasets` when `test_size=0` AND `reverse_train_test_order=True`, mirroring the existing `causal_mode`/reverse rejection pattern. The `timeseries_split` path already rejects `test_size < 1` upstream of the swap.

Behavior change in the deprecated path: `support_policy='raise'` now correctly raises on actual-train insufficient support; `support_policy='fallback'` now correctly warns.

Reviewed by three parallel Oracle passes (math + algorithmics + scope/reachability; Python state-of-the-art + harmonization + implementation elegance; documentation + terminology + completeness) at design stage and again post-implementation, each citing upstream evidence from `freqtrade/freqai/`.

Follow-up from PR #80 review, deferred during PR #90.

Closes #92.