fix: fill missing fully qualified syntax in prompt_handler macros

[moroviintaas]

Motivation and Context

Some syntax generated by macro #[prompt_handler] was not fully qualified.
I needed to use them in my user code, so the macro does not break. This include:

• rmcp::model::GetPromptResult
• rmcp::modelListPromptsResult
• rmcp::model::PaginatedRequestParams
• rmcp::RoleServer
• rmcp::service::RequestContext

How Has This Been Tested?

1. Modified locally examples/servers/src/common/counter.rs, removing imports from rmcp - fully qualified broken idents in examples.
2. Checked that build fails, because missing types with hint to import them.

 cargo test --workspace --examples --features server --features client

3. Applied this fix.
4. Checked that tests finish with success:

cargo test --workspace --examples --features server --features client

Breaking Changes

This commit probably does not introduce braking changes.
I haven't changed macros that use McpError, which is then imported in examples with rmcp::ErrorData as McpError.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

It seems there are still some macro code that forces user to import:

use rmcp::ErrorData as McpError

but I am not sure if fixing it would not be a breaking change.