Create separate SynchronizerId type, mirroring PartyId

[ayushsingh82]

Summary

• synchronizerId is passed around as a bare string in several places even where a sibling partyId parameter already uses the PartyId type from core-types.
• Added a SynchronizerId zod schema/type in core/types/src/index.ts, following the exact same pattern as PartyId (schema + z.infer type + example constant).
• Applied it at the sites that already sit right next to a PartyId-typed value:
  • SDKContext.defaultSynchronizerId (sdk/wallet-sdk/src/wallet/init/types/context.ts)
  • CreatePartyOptions.synchronizerId (sdk/wallet-sdk/src/wallet/namespace/party/external/types.ts)
  • SignedPartyCreationService.allocate()'s synchronizerId param (.../party/external/signed.ts, which already imports PartyId)
  • MergeDelegationNamespace.setup()'s synchronizerId param (.../token/utxos/mergeDelegation.ts, same file already imports PartyId)

I deliberately left the ~200 other bare synchronizerId: string occurrences elsewhere in the repo as-is — the large majority are in auto-generated OpenAPI/AsyncAPI/protobuf client code (core/ledger-client-types/src/generated-clients/**, core/ledger-proto/src/_proto/**) that would just get overwritten on the next codegen run. This mirrors how PartyId itself isn't retrofitted everywhere either (grep -rn "partyId: string" still finds ~27 files outside the generated clients).

Note: like PartyId, SynchronizerId isn't a branded type (z.infer of a z.string() schema resolves structurally to string), so this is a type-level-only, zero-runtime-behavior change everywhere it's applied.

Fixes #522

Test plan

• Added unit tests for the SynchronizerId schema (valid id, missing :: separator, too-short) in core/types/src/index.test.ts — 14/14 passing in that suite.
• npx vitest run --project node src/wallet/namespace/party/party.test.ts (wallet-sdk) — 18/18 passing.
• eslint and prettier --check clean on all 6 changed files.
• tsc --noEmit clean on every touched file (pre-existing unrelated module-resolution errors elsewhere in wallet-sdk come from other packages needing a full monorepo build, not from this change).

[ayushsingh82]

@alexmatson-da whenever you have a chance, would appreciate a look at this one.

[mjuchli-da]

Minor correction needed

[mjuchli-da]

Example should not be part of the types library and only be used in tests

[ayushsingh82]

@mjuchli-da Done — moved SYNCHRONIZER_ID_EXAMPLE out of the types library and into index.test.ts as a local test-only constant. Pushed in efd2d19.