ci: weekly fuzz_import_csv; testing.md: import in progress

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX

.github/workflows/scheduled.yml

@@ -22,7 +22,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        target: [fuzz_journal_line, fuzz_entry_validate, fuzz_op_sequence, fuzz_core_serde, fuzz_store_open, fuzz_store_replay]
+        target: [fuzz_journal_line, fuzz_entry_validate, fuzz_op_sequence, fuzz_core_serde, fuzz_store_open, fuzz_store_replay, fuzz_import_csv]
     steps:
       - uses: actions/checkout@v4
       - uses: jdx/mise-action@v2