Add fixed-size type support for IdPkTs and EventRef

- Update nostr dependency to v1.0.11 with new types package
- Add IDFixed(), PubFixed(), IDHex(), PubHex() methods to IdPkTs
- Add EventRef type: 80-byte stack-allocated event reference
- Add ToEventRef()/ToIdPkTs() conversion methods
- Update tests to use IDHex() instead of hex.Enc(r.Id)

EventRef provides:
- Copy-on-assignment semantics (arrays vs slices)
- Zero heap allocations for event reference passing
- Type-safe fixed-size fields (EventID, Pubkey)

Files modified:
- go.mod, go.sum: Update nostr to v1.0.11
- pkg/interfaces/store/store_interface.go: Add methods and EventRef type
- pkg/interfaces/store/store_interface_test.go: New test file
- pkg/database/binary_tag_filter_test.go: Use IDHex()
- pkg/neo4j/fetch-event_test.go: Use IDHex(), PubHex()

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

pkg/neo4j/fetch-event_test.go

@@ -339,11 +339,11 @@ func TestGetFullIdPubkeyBySerial(t *testing.T) {
 		t.Fatal("Expected non-nil result")
 	}
 
-	if hex.Enc(idPkTs.Id) != hex.Enc(ev.ID[:]) {
+	if idPkTs.IDHex() != hex.Enc(ev.ID[:]) {
 		t.Fatalf("ID mismatch")
 	}
 
-	if hex.Enc(idPkTs.Pub) != hex.Enc(ev.Pubkey[:]) {
+	if idPkTs.PubHex() != hex.Enc(ev.Pubkey[:]) {
 		t.Fatalf("Pubkey mismatch")
 	}