chore: align with the org standard (TS1, CI4, CI5)

[lesnik512]

Brings the repo in line with the standard, from the org conformance audit:

• TS1: set testpaths = ["tests"]
• CI4: run the lint job on the floor Python (3.11, was 3.13)
• CI5: install with just install in the pytest job, as every other repo does

just lint-ci passes on 3.11 locally; tests need the service containers, so CI is the check.

[github-actions]

Benchmark gate

✅ gate passed

scenario	msg/s	delete/msg	WALrec/msg	WALB/msg	fpi	upd	del	dead_tup
consumer/w1/b10	963	1.000	6.79	917	242	5000	5000	10000
consumer/w1/b100	978	1.000	6.83	920	243	5000	5000	10000
consumer/w2/b10	1115	1.000	6.79	953	242	5000	5000	10000
consumer/w2/b100	1318	1.000	6.73	958	243	5000	5000	10000
consumer/w4/b10	989	1.000	6.82	995	261	5000	5000	10000
consumer/w4/b100	1493	1.000	6.87	1040	244	5000	5000	10000
consumer/w1/b100/tfbs100	5059	0.010	6.07	1116	243	5000	5000	10000
producer/w1/b100	2174	0.000	3.04	584	0	0	0	0

Gated (fails the build): delete_calls + tuple counters (upd/del/ins) + the producer's insert_calls, exact; select_calls within +2; wal_records within a 10% band. msg/s, WAL bytes and total calls are informational (timing/FPI noise).