fix(038_02_01, 038_08_03): Location is a URI reference + an actually-invalid q (also un-leaks 041 counts)

038_02_01 stored the raw Location header as the subscription id; Location is a URI reference (RFC 9110 § 10.2.2) carrying the resource path, so the follow-up retrieve and the teardown delete built doubled URLs and failed — leaking the created subscription into the 041_* count assertions. The id is now the last path segment, and the retrieve comparison ignores the clause-12.4.7 Additional Members (root level and inside 'notification') like its 038_01/038_03 siblings.

038_08_03's fixture used "q": "invalidQuery" — a bare attribute path, which the § 7.x ABNF (QueryTerm = Attribute) makes a VALID existence-predicate query that brokers must accept with 201. The fixture now sends "(invalidQuery" (unbalanced parenthesis), the same genuinely-invalid form 037_03_02 uses.

The notification_result_regex_expr variable and the assertionUtils.py threshold_to_diff_deeper=0 fix are re-declared identically to their origin branch (unmerged MR) — git deduplicates on merge.

Analysis recorded as testsuite-doubts.md #96.