fix(tasks): default getTaskResult to the generic tasks/result schema when none is given

[SAY-5]

client.experimental.tasks.getTaskResult(taskId) now falls back to GetTaskPayloadResultSchema when the caller omits the optional result schema, instead of forwarding undefined into validation.

Fixes #2742

Motivation and Context

The wrapper declares resultSchema?: T but hands it straight to Protocol.getTaskResult, whose parameter is required and goes into request() unchanged. With undefined the response path reaches isZ4Schema(undefined) in src/server/zod-compat.ts and throws TypeError: Cannot read properties of undefined (reading '_zod') from inside _onresponse, so it does not surface as a rejection of the awaited call either.

getTask and listTasks already pass a default schema; tasks/result has one too (GetTaskPayloadResultSchema, the loose ResultSchema), it was just never wired up. The type parameter now defaults to that schema so a schema-less call is typed as GetTaskPayloadResult rather than resolving through the bare AnyObjectSchema constraint. Callers that pass a schema are unaffected.

How Has This Been Tested?

Extended the existing should query task result from server using getTaskResult test in test/client/index.test.ts to also fetch the same task without a schema. It fails on v1.x with the reported _zod TypeError before the change. npm run typecheck, npm run lint and the client, server and task-lifecycle suites pass locally.

Breaking Changes

None.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

Based on v1.x since that is where the reported code lives.

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