docs: replace emoji link headings with a Links section (RM3)

[lesnik512]

Replaces the emoji link headings at the end of the README with a plain ## Links list, following RM3 in the org standard (modern-python/.github#132). The links and their URLs are unchanged, and the "Part of modern-python" section still follows.

The headings showed up as empty sections in GitHub's README outline and on the PyPI page.

[github-actions]

Benchmark gate

✅ gate passed

scenario	msg/s	delete/msg	WALrec/msg	WALB/msg	fpi	upd	del	dead_tup
consumer/w1/b10	1351	1.000	6.72	921	242	5000	5000	10000
consumer/w1/b100	1433	1.000	7.11	1154	243	5000	5000	10000
consumer/w2/b10	1626	1.000	6.72	924	242	5000	5000	10000
consumer/w2/b100	1912	1.000	7.11	1154	243	5000	5000	10000
consumer/w4/b10	1631	1.000	6.75	948	242	5000	5000	10000
consumer/w4/b100	1922	1.000	7.11	1153	243	5000	5000	10000
consumer/w1/b100/tfbs100	5835	0.010	6.11	1130	243	5000	5000	10000
consumer/w1/b100/interval1-10	1469	1.000	7.17	1196	265	5000	5000	10000
producer/w1/b100	3002	0.000	3.04	597	1	0	0	0
producer/w1/b100/ppt1	973	0.000	4.04	635	0	0	0	0

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