feat (bindings/go): add AnchorMany to batch anchor payloads in one event

[ykinkov]

Changes

Adds AnchorMany to bindings/go — a batched counterpart to the existing Anchor that commits multiple payloads into the KEL in a single interaction (ixn) event.

• AnchorMany anchors the Blake3-256 digest of every payload in a single ixn. Each payload stays individually verifiable with the existing VerifyAnchor — as with Anchor, only the digest is committed to the KEL, never the payload, so verification remains byte-exact.
• Extends the anchor example (examples/anchor/main.go) with a batch section that anchors a set of keys via AnchorMany in one event, then verifies one of them individually.

Running locally

The anchor example (which exercises AnchorMany) needs only Postgres — no witness or watcher.

1. Start Postgres (from bindings/go):

  docker compose up -d postgres

2. Run the anchor example (from bindings/go):

cd examples/anchor
DATABASE_URL=postgres://postgres:postgres@localhost:5432/keri_go go run .

Expected output includes the batched anchor:

Anchored 3 WireGuard keys in one event
Batched key anchored: true

[ykinkov]

@mitfik, can you check this PR when you have the time?