fix: make _nuitka_astropy_patch a no-op outside Nuitka builds (fixes #151)

[thusser]

Closes #151 — the Nuitka workaround patch was breaking astropy's unit/coordinate parsing when running from source.

Root cause

patch_generic_unit_parser() claimed to be a no-op under a regular interpreter, but the wrapper functions it installs (patched_yacc_dict / patched_lex_dict) add one stack frame, which shifts astropy 7.2.2's frame-level bookkeeping: astropy/utils/parsing.py calls get_caller_module_dict(2) directly and its _patch_ply_module wrapper adds two more levels. The extra frame makes the walk land on astropy's parsing wrapper instead of the grammar-defining frame, so the fallback fired on plain CPython — instrumented runs showed both walk(2) and walk(4) coming back without tokens.

The substituted vendored grammar was also never registered in sys.modules, so PLY's validate_pfunctions → inspect.getsourcefile(None) died with TypeError ... got NoneType while importing astropy.units (Unit("m / (s)")). With a faithful Nuitka simulation (empty f_locals on the PLY walks), the angle parser in astropy.coordinates.angles.formats gets the generic-unit grammar substituted and rejects every coordinate — the reporter's exact "Cannot parse first argument data" / "Invalid coordinates" symptom.

Changes

• patch_generic_unit_parser() is now a strict no-op outside Nuitka builds. It returns immediately unless running compiled; pyobs_gui/__init__.py passes compiled="__compiled__" in globals() (evaluated in the module guaranteed compiled in the binary).
• Frame compensation: the patched walks now call the originals with levels + 1, restoring the exact frame the unpatched walk would inspect — the fallback only fires when the walk genuinely lacks the grammar (compiled frames without f_locals). Verified: with the patch force-installed under CPython, the fallback fires 0 times and parsing works.
• Registered grammar module: the vendored namespace is registered in sys.modules and its __file__ stub is materialized, so a real Nuitka grammar rebuild no longer dies in PLY validation (tables get written to the existing scratch dir).
• Scoped fallback: the generic-unit grammar is only substituted for astropy.units.format.generic; angle/cds/ogip builds now fail loudly instead of silently parsing with the wrong grammar.

Verification

• Issue _nuitka_astropy_patch breaks coordinate parsing when running from source #151 repro (SkyCoord("18h36m56.33634889s +38d47m01.28024248s", frame=ICRS, unit=(u.hour, u.deg)) after patch_generic_unit_parser()) passes from source.
• Forced-compiled install under CPython: parses fine, 0 fallback firings.
• Simulated Nuitka: generic-unit parsing works, grammar tables rebuilt into the scratch dir; angle parsing fails cleanly (angle grammar is a documented, still-open limitation for the binary).
• Existing suite: 43/43 tests pass; ruff and black clean.