* Replace pickle with msgspec MessagePack serialization

- Use msgspec for chipdb serialization (faster, typed)
- Deduplicate grid tiles: grid stores ttyp indices, tiles dict maps to Tile objects
- Add Device.__getitem__/__setitem__ for grid[row, col] -> Tile access
- Update all grid iteration patterns across chipdb, gowin_pack, gowin_unpack, etc.
- Update Makefile, CI workflow, setup.py for .msgpack.gz format

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Switch chipdb compression from gzip to lzma

LZMA compresses msgpack data ~5x better than gzip (2.8 MB vs 15.8 MB
total) while decompressing slightly faster. This shrinks the PyPI
package significantly with no load time penalty.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Add cattrs+msgpack fallback for pure Python environments

When msgspec is not available (e.g. PyPy), fall back to cattrs+msgpack
for deserializing chip databases. Only two custom cattrs hooks needed:
- Union: cattrs refuses ambiguous unions like Union[int, str]
- bytearray: msgpack returns bytes, need conversion to bytearray

Also narrow Bel type annotations based on exhaustive data analysis:
- Bel.flags keys: Dict[Union[int, str], ...] -> Dict[int, ...]
- Bel.modes keys: Dict[Union[int, str], ...] -> Dict[str, ...]

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Fix numpy truth-value errors and use [fast] extra in CI

Replace truthiness checks on variables that hold numpy arrays with
explicit None checks to avoid "ambiguous truth value" ValueError.

Remove the [msgspec] extra (redundant with [fast]) and use [fast]
for all CI boards except tangnano which tests the [pure] path.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Make C extension deps the default, document pure Python alternative

Move msgspec/numpy/crcmod to install_requires so they are installed by
default. Document `pip install --no-deps apycula msgpack cattrs` in the
readme for platforms without C extension support.

Simplify CI to match: most boards use default install, tangnano tests
the pure Python path.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>