fix: hide validator provider types from root declarations

[chaochaoweb3]

Summary

• remove validator provider class/draft type re-exports from the shared public root barrel
• keep validator provider types available from the explicit validators/ajv and validators/cf-worker subpaths
• add client/server barrel-clean regression coverage for both ESM and CJS root declarations

Fixes #2391.

Validation

• corepack pnpm install --frozen-lockfile
• corepack pnpm --filter @modelcontextprotocol/client build
• corepack pnpm --filter @modelcontextprotocol/server build
• corepack pnpm --dir packages/client exec vitest run test/client/barrelClean.test.ts
• corepack pnpm --dir packages/server exec vitest run test/server/barrelClean.test.ts
• corepack pnpm --filter @modelcontextprotocol/client typecheck
• corepack pnpm --filter @modelcontextprotocol/server typecheck
• git diff --check

[changeset-bot]

🦋 Changeset detected

Latest commit: b2978a0

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

This PR includes changesets to release 2 packages

Name	Type
@modelcontextprotocol/client	Patch
@modelcontextprotocol/server	Patch

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commit: b2978a0