Escape-baseline keys are fragile across Python versions (comprehension frame names, PEP 709)

Follow-up from PR #942 (review item P2, https://github.com/astropy/ccdproc/pull/942#pullrequestreview-4695447403).

Baseline keys in `ccdproc/tests/array_escape_baseline.txt` include the frame *function name* of the escape site. Those names are not stable across Python versions:

- List comprehensions have their own frame named `` on Python < 3.12, but are inlined into the enclosing function on 3.12+ (PEP 709), so the same escape keys differently depending on the interpreter.
- Generator expressions and lambdas key as `` / `` on all versions, which are ambiguous within a file.

The enforce CI job (`py312-alldeps-dask-enforce`) runs on Python 3.12, so a contributor who regenerates the baseline with `CCDPROC_WRITE_ESCAPE_BASELINE=1` on Python 3.11 produces mismatched keys: CI then reports spurious NEW-escape failures (the 3.12 spelling is missing) plus spurious stale entries (the 3.11 spelling is never observed).

Fix options:
1. Normalize comprehension-style frame names (``, ``, ``, and possibly ``/``) to the enclosing function's name when recording escape sites, so keys match across versions; or
2. Document a Python floor (>= 3.12) for baseline regeneration in `docs/array_api.rst` and in the baseline file header, and optionally have write mode refuse to run on older interpreters.

Start with PR #942's review item and ccdproc/tests/array_escape_baseline.txt, then inspect the escape-site recording used by CCDPROC_WRITE_ESCAPE_BASELINE=1. Compare behavior on Python 3.11 and 3.12, including the enforce CI job. Done means baseline keys are stable across supported versions, or the Python floor and write-mode restriction are documented in docs/array_api.rst and the baseline header.

Written by the indexing model from the issue text.