feat(mcpserver): add add_resource_template() for programmatic template registration

[pasmud]

Closes #3333

Summary

Adds add_resource_template() to both ResourceManager and MCPServer so a ResourceTemplate instance can be registered programmatically, without going through the @resource decorator.

server = MCPServer("...")

# Configure resources in separate modules
server.add_resource_template(
    ResourceTemplate.from_function(users.list_users, "resource://users/{id}")
)

ResourceManager.add_resource_template() mirrors add_resource() semantics: registering a template whose uri_template already exists logs a warning (respecting warn_on_duplicate_resources) and returns the existing template. add_template() now delegates to the new method so there's a single registration path.

Changes

• src/mcp/server/mcpserver/resources/resource_manager.py: new add_resource_template(); add_template() delegates to it
• src/mcp/server/mcpserver/server.py: new thin add_resource_template() on MCPServer
• docs/servers/resources.md: document programmatic template registration
• Tests: registration, duplicate handling (warn + return existing, opt-out), template resolution through get_resource, and listing via list_resource_templates()

Verification

• ruff format / ruff check / pyright: clean
• ./scripts/test: 5747 passed, 8 skipped, 1 xfailed; coverage 100%. (The single failure, test_permission_error, is a root-user environment artifact that also fails on origin/main here; it passes in CI.)
• pre-commit: all hooks pass

Types of changes

• New feature (non-breaking change which adds functionality)

[github-actions]

Thanks for the contribution. This repository only keeps pull requests open when they're linked to an issue that a maintainer has assigned to the author — CONTRIBUTING.md explains why and how we work. This PR has been closed for now because you aren't currently assigned to #3333.

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