Fix BatchRotatingKVCache rotated flag deserializing to True

[odysa]

Fixes #1250.

meta_state round-trips self.rotated through str() on save and bool() on load, but bool("False") is True (any non-empty string is truthy). A cache saved with rotated=False reloads as rotated=True, silently corrupting the rotation mask in subsequent make_mask calls.

Fix: parse the bool by string comparison.

- self.rotated = bool(v[3])
+ self.rotated = v[3] == "True"

Added a regression test (test_save_load_batch_rotating_cache) that round-trips both rotated=False and rotated=True. Verified the test fails on main and passes with the fix.