PY-PORT-2d: port tarball_build_errors.py to aprender-ci-tools tarball-build-errors (C301) #4797

Sub-ticket of #4741 (PY-PORT-2, operator rule C301: no Python in the build).

Port scripts/lib/tarball_build_errors.py (74 lines, stdlib) to crates/aprender-ci-tools as the subcommand tarball-build-errors LOG.

Acceptance:

1. aprender-ci-tools tarball-build-errors LOG prints byte-identical stdout to the .py and exits with the same code (0, 1, 2, 3 or 4) on every case of a parity table in scripts/tests/ci_tools_py_parity_test.sh. The table covers each exit class, the HOST patterns, the 20/5/10 truncation caps, a version holding - (longest-prefix crate match), \r / \x0b / U+2028 line breaks (Python splitlines), invalid UTF-8, a missing file, and a wrong argument count. The harness keeps its planted-mismatch check, so it cannot pass vacuously.
2. cargo-mutants on the new module: every surviving mutant is either killed by a new case or listed with a reason.
3. Callers are NOT switched in this ticket. scripts/package_tarball_build.sh sits on the publish/clean-room gate path, and gate tools ship one train earlier (N-1). The .py stays until a later ticket switches the callers.

Branch-only. No PR; the head is handed to the PMAT-4741 batch.