SEP-2164: Standardize resource not found error code (-32602)

[mikekistler]

Is your feature request related to a problem? Please describe.

Implement support for SEP-2164, which is planned for inclusion in the 2026-06-30 version of the MCP spec.

Describe the solution you'd like

Compliance with the 2026-06-30 version of the MCP spec within two weeks of its release.

[jayaraman-venkatesan]

@mikekistler I can pick this up
My triage

1. Deprecate McpErrorCode.ResourceNotFound (-32002) with an [Obsoletel attribute and diagnostic
2. Change the server to throw McpErrorCode. InvalidParams (-32602) instead of ResourceNotFound for missing resources