Convert tool/prompt schemas eagerly at register time instead of on tools/list

Currently standardSchemaToJsonSchema() is called lazily inside the tools/list request handler (mcp.ts:145, 153), re-converting every tool's schema on every list request.

Moving this to registerTool() / registerPrompt() time and caching the JSON Schema result on RegisteredTool/RegisteredPrompt would:

• Surface schema errors (e.g. cycle detection from #1563) at dev time when the tool is registered, not at runtime when a client first calls tools/list
• Avoid re-converting identical schemas on every tools/list call
• Match Go SDK and fastmcp, which both process schemas at registration time

Scope: registerTool, registerPrompt, the tools/list and prompts/list handlers, and RegisteredTool.update() / RegisteredPrompt.update() (need to re-convert when schema changes).

Related: #1563 (where this came up)

Start in mcp.ts at the tools/list handler around lines 145 and 153, then trace registerTool(), registerPrompt(), RegisteredTool.update(), and RegisteredPrompt.update(). Move schema conversion to registration and update paths while preserving the list responses and ensuring schema changes are re-converted. Done means schemas are not re-converted on each tools/list or prompts/list request and conversion errors surface during registration.