fix(sqlite): write the Windows lock byte in binary; drop source-text asserts

On native Windows the text-mode ``handle.write("\n")`` that seeds an empty
``--lock-file`` is translated to ``\r\n``, so a fresh lock file is two bytes
and the msvcrt regression test fails on the platform it protects. Seed the
file with ``os.write(fd, b"\0")`` on the descriptor instead: exactly one byte
whatever the text-mode newline translation. The Windows-branch tests now run
under a ``\n`` -> ``\r\n`` translating ``open`` so this failure reproduces
on any host.

Remove the two ``... not in src`` assertions added for the previous review
from test_issue2628: the behaviours they hinted at (every missing-index
projection uses the pre-aggregated ordering; listing never creates an
index) are already asserted through query plans, result equivalence and
``PRAGMA index_list`` in test_pr7445_readonly_review_followups.py,
test_state_db_readonly_readers.py and test_issue3887_index_prime.py.

scripts/ensure_state_db_read_indexes.py

@@ -67,9 +67,11 @@ def _exclusive_lock(lock_file):
             # Lock one byte at offset 0 without blocking; raises OSError when held.
             # ``a+`` may have just created an empty file, and Windows cannot lock
             # a range beyond EOF, so make sure byte 0 exists first. An existing
-            # (deployment-owned) lock file is left untouched.
+            # (deployment-owned) lock file is left untouched. Write the byte on
+            # the descriptor: a text-mode ``handle.write("\n")`` becomes two
+            # bytes (``\r\n``) on native Windows.
             if os.fstat(handle.fileno()).st_size == 0:
-                handle.write("\n")
+                os.write(handle.fileno(), b"\0")
                 handle.flush()
             handle.seek(0)
             msvcrt.locking(handle.fileno(), msvcrt.LK_NBLCK, 1)