Re: [PATCH v2] fetch2/local: verify checksums for file:// urls

Apologies, the "Changes in v2:" section in v2 ships with two literal
b4 placeholder lines starting with "EDITME: ..." that I forgot to
fill in before sending. Please disregard those two lines. The actual
changes from v1, addressing Paul Barker's review
(lore.kernel.org/r/[email protected]):

- Commit body trimmed; UNINATIVE_URL trigger now leads paragraph 1
  (Paul flagged this was missing from v1).
- Dropped the long historical commit references (b8b14d975a25,
  6424f4b7e9c1, 4b8de2e7d126) from the commit body.
- rename_bad_checksum moved from a module-level helper in
  bb/fetch2/__init__.py onto the FetchMethod class; Local overrides
  it as a no-op so a ChecksumError surfaces without renaming files
  under the user's source tree. Four callsites updated to
  ud.method.rename_bad_checksum(...). No "ud.type == 'file'" special
  case in __init__.py.
- Inline comment in local.py trimmed from ~10 lines to 3.
- Tests reduced to two keepers in FetcherLocalTest:
  - test_local_checksum_match: simpler comment; same assertion.
  - test_local_checksum_mismatch: dropped the os.listdir loop,
    replaced with a direct assertFalse on the specific
    bad-checksum sibling path.
  Dropped: test_local_no_checksum_no_donestamp,
  test_local_checksum_mismatch_md5, test_local_checksum_named,
  test_local_checksum_directory_ignored (the directory-with-bad-
  checksum case Paul noted should raise; left out of this patch
  rather than widening scope).

Thanks,
Jhonata