[ ContextVM/sdk ] feat(payments): synthesize JSON-RPC error on payment_rejected and add default TTL

Add support for synthesizing a JSON-RPC error response when the server sends
payment_rejected, allowing the MCP request to fail immediately instead of
hanging until the timeout. Also add defaultPaymentTtlMs option to keep the
client-side request alive for the same duration the server will wait when
the payment_required notification omits the ttl field.

Add rejectPrice() and quotePrice() helper factories to types.ts for safer
price resolution. Add duplicate PMI handler/processor warnings. Include ttl
https://github.com/ContextVM/sdk/commit/3f90064ef17f65176e27f842bc775b4e5ef787ee