feat(identity): add the default multichain identity client

[Wondertan]

Summary

Stacked on #64. Starts @libid/identity: libID identities across every ledger a client serves, built on @libid/ledger's multichain client. The ledger package owns the catalog, chain access and the indexer protocol; this package owns the identity registry's meaning.

// Every pinned libID ledger, read through the connected wallet.
const identity = createIdentityClient()

// One list, keyed by ledger objects: an entry for a pinned ledger configures it, any other adds it.
createIdentityClient({
  indexer: 'https://testnet.names.lib.id',
  ledgers: [
    { ledger: Ledgers.EdenTestnet, fee: { amount: 10n ** 15n, recipient } },
    { ledger: anvil, rpc: 'http://127.0.0.1:8545', indexer: false },
  ],
  exclude: [], // pinned ledgers to leave out
})

• Defaults: with no options, it serves every pinned ledger (Eden testnet and Sepolia today) that has the identity registry (identityRegistry, the IdentityRegistry contract). It reads through the connected wallet and charges no fee. libID pins no RPCs; an entry's rpc enables reads before a wallet connects and lets wallets be offered the chain.
• Entries:
  • An entry can set rpc and explorer, reach the ledger through another ledger client, replace or turn off the names indexer, and carry that ledger's integrator fee. libID defines no fee.
  • Entries never change a pinned ledger's deployments; the ledger client refuses that.
  • A ledger that is both configured and excluded, or configured twice, is rejected.
• Validation: fees must be positive, and the recipient is canonicalized. Configured endpoints are validated.
• Indexer: given by origin, with identity supplying the identityRegistry deployment. On a ledger with one, identity lists come from the indexer or fail; there is no fallback.
• Client surface: ledgers, ledger(chain), walletRequirements, fee(ledger).

Identity reads, readiness and durable bindings follow in stacked PRs. IdentityError arrives with the first operation that throws one.

Verification

• pnpm --filter @libid/identity build, typecheck, test: 11 tests pass.
  • The zero-config default, and configuring and adding ledgers from one list.
  • Excluding, delegating to another client, and refusing a changed pinned ledger.
  • Duplicate and conflicting entries.
  • Registry and endpoint requirements, wallet-only ledgers, and fee and indexer validation.
• Mutation checks, each caught:
  • entries configuring pinned ledgers;
  • entries adding others;
  • exclude;
  • the duplicate guard;
  • the configured-and-excluded guard.
• Workspace-wide pnpm build, typecheck, test (ledger 104, popup 154, identity 11, ceremony 996), lint, fmt:check and test:packages pass on main at cbe7f35.
• The package stays private, so the published-package check does not cover it; its build follows the other packages' build-package.ts.