The TDSE consistency cache uses a Linux-style directory on macOS and Windows #583

`solprop.driver.tdse_consistency.cache_directory` keeps its cache in `$XDG_CACHE_HOME/solprop` or `~/.cache/solprop` on every platform (`src/solprop/driver/tdse_consistency.py`). SEP 46's calibration store, added in #582, follows each platform's convention instead (`native/src/solprop_native/_store.py`, `cache_directory`):

• `~/Library/Caches/solprop` on macOS;
• `%LOCALAPPDATA%\solprop\Cache` on Windows;
• the XDG location on Linux.

Both honour `SOLPROP_CACHE_DIR`. Without it, on macOS and Windows solprop's two caches end up in different places, and the TDSE one is outside the directory the platform clears and backs up as a cache.

Proposed: have the TDSE cache take the store's directory (`solprop.calibration.store_directory()`), keeping its `tdse-consistency` subfolder. An existing cache in the old place would just be rebuilt once.

Found while implementing SEP 46 phase 0 (recorded there as Q1).