Bug A: #processOne's catch collapsed EVERY handler throw to -32603, ignoring
err.code — so domain errors (a handler throwing { code: -32004 } not-found,
-32009 conflict, etc.) were impossible. Now honor a JSON-RPC-shaped error
(numeric code) before the -32603 fallback.

Bug B: no ./rpc/* export subpath — `import from '@c9up/ream/rpc/provider'`
failed ERR_PACKAGE_PATH_NOT_EXPORTED (the code shipped in dist but wasn't
exported). Add ./rpc/provider + ./rpc/router (mirroring ./events/provider).