fix(python): pin only the 3.14 and 3.15 magics checked locally

Keep magic 3627 (CPython 3.14.6) and 3666 (CPython 3.15.0b3), whose code
layout and inline-cache tables match those interpreters' opcode tables and
whose decoded code objects match marshal.loads across a stdlib sample. Leave
the 3.15.0a8 magic 3663 unpinned, since no 3.15.0a8 interpreter was available
to check it, and regenerate the 3.15 slice fixture with 3.15.0b3.

Co-Authored-By: gensokyo-dev <342580529+gensokyo-dev@users.noreply.github.com>

docs/python-pyc.md

@@ -81,11 +81,10 @@ The inline Evidence result contains the artifact path, SHA-256, and byte length.
 
 - `magic`, the 16-bit little-endian field;
 - `python_version` and `code_layout`, mapped from the pinned CPython marshal
-  table (`py37`, `py38`, or `py311`): 3.7–3.13, plus three 3.14 and 3.15
-  magics: 3627 (3.14.4) and 3663 (3.15.0a8), both read back from real
-  interpreters, and 3666 (3.15.2), checked with real 3.15.2 release bytes
-  decoded by the 3.15.0a8 interpreter (3.15.2 itself was not run). Other 3.14
-  and 3.15 pre-release magics are not pinned and are unsupported. 3.11 alpha
+  table (`py37`, `py38`, or `py311`): 3.7–3.13, plus the 3.14 magic 3627 and
+  the 3.15 magic 3666, each checked against a real interpreter (CPython 3.14.6
+  and 3.15.0b3). Other 3.14 and 3.15 pre-release magics are not pinned and are
+  unsupported. 3.11 alpha
   magics before 3494 used other code layouts and are unsupported. The
   3.7.0a1/a2 magics 3390/3391 used 12-byte headers and are outside this
   reader's supported format;