feat(gns): GNS (Gno Name Service) realm at r/moul/gns/v1

[moul]

Adds GNS (Gno Name Service) as the first real contract in this repo, at the
versioned path gno.land/r/moul/gns/v1.

GNS is an ENS-equivalent naming system expressed as one realm (registration,
commit–reveal, expiry/grace, typed + arbitrary records, forward-verified
reverse/primary names, subnames with policies + emancipation, operators,
pagination, events, two-step admin, Render explorer). Full details in
r/moul/gns/v1/README.md.

Notable in this PR

• Versioned per the repo rule (…/gns/v1); Render links point at /v1.
• Adapted to current-master avl: upstream avl/v0.Get now returns a single
  value (existence via Has), not (any, bool). GNS was written against the
  older cached API; a small treeGet helper bridges it. This is exactly the
  master-fidelity this repo exists to enforce.
• Dependencies vendored (avl/v0, ufmt/v0, testutils/v0) into
  vendor/ — make deps also pulls test-only deps so gno test is autonomous.
• Client caching guidance (user↔address: 1h on match, 1min on no-match)
  documented in the contract README.
• Catalog + README table updated via make gen.

Verification

make lint + make test clean locally (gns 0.6s, all green) against a
gnolang/gno master checkout.

Note: fixed an infinite-recursion bug in the shared recordMutation helper
that had been introduced by an over-broad refactor (it called itself); this
was the cause of the earlier OOM/hang. Now each record setter shares the
preamble correctly.

[github-actions]

go tool gnocontracts report -base origin/main

📦 gno-contracts PR report

1 new · 0 updated package(s) — 13 file(s), +3700/-0 lines

New packages

• 🆕 r/moul/gns/v1 — +3700/-0, 🧪 44 test(s)

Signals

• ⚠️ r/moul/gns/v1 uses unsafe
• 🔥 r/moul/gns/v1 handles coins (banker)

🤖 auto-generated; checks grow over time.