fix(uri-template): preserve percent-encoded triplets in reserved expansions

[takagibit18]

Reserved and fragment expansions currently turn %20 into %2520, changing a value that already contains a URI escape. Preserve valid %HH sequences after encodeURI() for those two operators.

The behavior follows RFC 6570 section 3.2.1. Regression tests cover lowercase hex digits, encoded percent signs, list elements, fragment values and malformed escapes. A simple-expansion test checks that its percent sign is still encoded. The changeset covers the client and server packages, which publicly export UriTemplate.

Closes #2920.

Validation

• Core-internal: 1528 tests passed with the repository's Vitest 4.1.2 configuration using --configLoader runner.
• pnpm lint:all, pnpm typecheck:all, and pnpm build:all: passed.
• The issue reproducer returns the expected output with this patch.
• The Workers compatibility test passed when run outside the sandbox.

The full workspace test run on Windows has failures in the codemod symlink-cycle test and two stdio shutdown-escalation cases that wait for a SIGTERM marker.

[changeset-bot]

🦋 Changeset detected

Latest commit: d7d4888

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 6 packages

Name	Type
@modelcontextprotocol/client	Patch
@modelcontextprotocol/server	Patch
@modelcontextprotocol/codemod	Patch
@modelcontextprotocol/core	Patch
@modelcontextprotocol/server-legacy	Patch
@modelcontextprotocol/core-internal	Patch

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commit: d7d4888