Hashbrown native table engine

Original source: hashbrown 0.17.1, https://github.com/rust-lang/hashbrown
Copyright (c) 2016 Amanieu d'Antras
Original grant: MIT OR Apache-2.0, retained without alteration.
The original license texts are in LICENSES/MIT.txt and LICENSES/Apache-2.0.txt.

Modifications Copyright (c) 2026 Blackcat Informatics Inc.
Modifications to inherited engine files are also offered under MIT OR Apache-2.0.
These files are modified inherited source, not unchanged upstream source.
All inherited Rust files identify this notice in their opening source header.

Changes to inherited files: fix the upstream allocator/integration profile in
source, use the existing workspace fixed-key default without a hasher dependency,
retain target-selected kernels, relocate module and documentation paths,
exclude dependency-heavy upstream test modules, and integrate native governed
work and transactional allocation with the shared Core table engine.
New wrapper and regression code carries its own first-party source headers.
UPSTREAM-SHA256.json records hashes of the original upstream source files.
