fix: React to upstream RC schema changes for form mode elicitation requests

[nbarbettini]

Motivation and Context

Reacting to upstream schema changes. Discussion: modelcontextprotocol/modelcontextprotocol#1863 (comment)

How Has This Been Tested?

Existing test coverage plus 1 new test.

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

A few review comments inline, below.

[pkg-pr-new]

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npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/sdk@1154

commit: bf5fbd1

[KKonstantinov]

LGTM!

One comment is on the cherry picked spec types, but we probably have no choice and it will be just temporary until the tasks SEP gets finalized on TS SDK and merged.

[felixweinberger]

Thanks for updating the PR! Please merge at your convenience :)