GH-99298: Clean up attribute specializations

[brandtbucher]

It's now impossible for specialization to raise exceptions.

Also, add an overly-cautious-but-inexpensive check for "unready" types when specializing STORE_ATTR, as we already do for LOAD_ATTR. Probably worth backporting this part manually?

No performance impact:

All benchmarks:
===============

Slower (20):
- mdp: 2.51 sec +- 0.02 sec -> 2.61 sec +- 0.01 sec: 1.04x slower
- pickle_list: 4.03 us +- 0.03 us -> 4.17 us +- 0.04 us: 1.04x slower
- scimark_sparse_mat_mult: 4.07 ms +- 0.07 ms -> 4.18 ms +- 0.06 ms: 1.03x slower
- pathlib: 17.3 ms +- 0.2 ms -> 17.7 ms +- 0.4 ms: 1.02x slower
- regex_effbot: 3.34 ms +- 0.02 ms -> 3.42 ms +- 0.03 ms: 1.02x slower
- telco: 6.25 ms +- 0.22 ms -> 6.39 ms +- 0.19 ms: 1.02x slower
- mako: 9.52 ms +- 0.06 ms -> 9.72 ms +- 0.05 ms: 1.02x slower
- regex_dna: 202 ms +- 1 ms -> 206 ms +- 1 ms: 1.02x slower
- django_template: 32.6 ms +- 0.5 ms -> 33.3 ms +- 0.3 ms: 1.02x slower
- float: 71.5 ms +- 0.8 ms -> 72.9 ms +- 1.1 ms: 1.02x slower
- fannkuch: 374 ms +- 11 ms -> 381 ms +- 15 ms: 1.02x slower
- deltablue: 3.19 ms +- 0.04 ms -> 3.25 ms +- 0.04 ms: 1.02x slower
- scimark_lu: 106 ms +- 2 ms -> 107 ms +- 4 ms: 1.01x slower
- coverage: 98.1 ms +- 1.2 ms -> 99.4 ms +- 1.2 ms: 1.01x slower
- nqueens: 81.1 ms +- 1.4 ms -> 82.2 ms +- 1.1 ms: 1.01x slower
- hexiom: 6.06 ms +- 0.02 ms -> 6.14 ms +- 0.03 ms: 1.01x slower
- xml_etree_iterparse: 104 ms +- 2 ms -> 106 ms +- 2 ms: 1.01x slower
- richards: 41.7 ms +- 0.7 ms -> 42.1 ms +- 0.9 ms: 1.01x slower
- scimark_fft: 311 ms +- 3 ms -> 313 ms +- 4 ms: 1.01x slower
- crypto_pyaes: 74.1 ms +- 0.7 ms -> 74.4 ms +- 0.8 ms: 1.00x slower

Faster (28):
- unpack_sequence: 46.1 ns +- 4.1 ns -> 42.5 ns +- 0.8 ns: 1.08x faster
- pidigits: 199 ms +- 0 ms -> 189 ms +- 0 ms: 1.05x faster
- coroutines: 25.5 ms +- 0.2 ms -> 24.6 ms +- 0.2 ms: 1.04x faster
- genshi_text: 21.1 ms +- 0.2 ms -> 20.4 ms +- 0.3 ms: 1.03x faster
- pycparser: 1.08 sec +- 0.02 sec -> 1.05 sec +- 0.02 sec: 1.03x faster
- logging_format: 6.34 us +- 0.10 us -> 6.23 us +- 0.07 us: 1.02x faster
- logging_simple: 5.75 us +- 0.08 us -> 5.66 us +- 0.06 us: 1.02x faster
- deepcopy_reduce: 2.94 us +- 0.04 us -> 2.89 us +- 0.04 us: 1.02x faster
- unpickle_pure_python: 204 us +- 2 us -> 201 us +- 1 us: 1.01x faster
- spectral_norm: 95.9 ms +- 3.8 ms -> 94.6 ms +- 2.6 ms: 1.01x faster
- pickle: 10.3 us +- 0.1 us -> 10.2 us +- 0.1 us: 1.01x faster
- pickle_dict: 31.3 us +- 0.1 us -> 31.0 us +- 0.1 us: 1.01x faster
- sympy_sum: 163 ms +- 1 ms -> 162 ms +- 1 ms: 1.01x faster
- sympy_str: 283 ms +- 4 ms -> 280 ms +- 4 ms: 1.01x faster
- regex_v8: 21.2 ms +- 0.1 ms -> 21.0 ms +- 0.1 ms: 1.01x faster
- generators: 78.7 ms +- 0.5 ms -> 78.0 ms +- 0.4 ms: 1.01x faster
- json_loads: 24.2 us +- 0.4 us -> 24.0 us +- 0.2 us: 1.01x faster
- json_dumps: 9.45 ms +- 0.18 ms -> 9.36 ms +- 0.13 ms: 1.01x faster
- sympy_expand: 457 ms +- 3 ms -> 453 ms +- 7 ms: 1.01x faster
- sympy_integrate: 20.3 ms +- 0.1 ms -> 20.2 ms +- 0.1 ms: 1.01x faster
- sqlglot_transpile: 1.63 ms +- 0.02 ms -> 1.61 ms +- 0.02 ms: 1.01x faster
- xml_etree_process: 53.2 ms +- 0.7 ms -> 52.8 ms +- 0.6 ms: 1.01x faster
- python_startup_no_site: 6.27 ms +- 0.01 ms -> 6.22 ms +- 0.01 ms: 1.01x faster
- genshi_xml: 46.9 ms +- 0.9 ms -> 46.6 ms +- 0.8 ms: 1.01x faster
- sqlglot_normalize: 106 ms +- 1 ms -> 105 ms +- 1 ms: 1.01x faster
- python_startup: 8.60 ms +- 0.01 ms -> 8.55 ms +- 0.01 ms: 1.01x faster
- 2to3: 246 ms +- 1 ms -> 245 ms +- 1 ms: 1.01x faster
- sqlglot_optimize: 50.9 ms +- 0.2 ms -> 50.7 ms +- 0.3 ms: 1.01x faster

Benchmark hidden because not significant (34): aiohttp, async_tree_none, async_tree_cpu_io_mixed, async_tree_io, async_tree_memoization, chameleon, chaos, deepcopy, deepcopy_memo, dulwich_log, go, gunicorn, html5lib, json, logging_silent, meteor_contest, mypy, nbody, pickle_pure_python, pprint_safe_repr, pprint_pformat, pyflate, raytrace, regex_compile, scimark_monte_carlo, scimark_sor, sqlglot_parse, sqlite_synth, thrift, tornado_http, unpickle, unpickle_list, xml_etree_parse, xml_etree_generate

Geometric mean: 1.00x faster

• Issue: Error handling for some instructions is incorrect #99298