Basics 0.4.10 — bounded TidesDB value-log retention

Add String::ownsMemory() to distinguish owned heap/mmap storage from mutable and read-only borrowed views. This lets asynchronous owners retain already-owned values without a redundant allocation and copy, while continuing to detach borrowed data. No String layout or existing copy/move behavior changes.

Validated the existing String test suite, including ownership checks across heap/mmap/view/read-only copy and move, with Clang 22 / C++26 and the pinned runtime dependencies.