testsuite: verify --fuzzy actually selects a basis

testsuite: verify --fuzzy actually selects a basis

Both fuzzy tests asserted only that the final file content matched, which a
full transfer that ignored --fuzzy would also satisfy -- so a broken fuzzy
basis selection would pass undetected. Drive rsync directly with --debug=FUZZY
and assert the generator reports the expected basis ("fuzzy basis selected
for <f>: <basis>", generator.c find_fuzzy): rsync2.c for fuzzy, and the
closest-named candidate archive-v1.tar for fuzzy-basis. fuzzy switches from
checkit() to a manual run plus verify_dirs() so the output can be captured.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>