Add invoke_dsc_function() and invoke_dsc_expression() tools to Server mode

[SteveL-MSFT]

PR Summary

• Complete renaming of loc string tags to server instead of mcp
• Add invoke_dsc_function() and invoke_dsc_expression() tools

rmcp crate doesn't allow direct use of serde_json::Value type, so need a wrapper enum to make it work.

PR Context

For you @ThomasNieto :)

[Copilot]

Pull request overview

This PR extends DSC “server” mode by adding two new JSON-RPC tools—invoke_dsc_expression and invoke_dsc_function—and updates server-mode localization keys to use the server.* namespace (instead of mcp.*).

Changes:

• Added invoke_dsc_expression and invoke_dsc_function tool implementations and registered them with the server tool router.
• Renamed server-mode i18n keys from mcp.* to server.* and updated call sites accordingly.
• Expanded Pester coverage to validate the new tools via tools/call.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
dsc/tests/dsc_server.tests.ps1	Adds Pester coverage for invoke_dsc_expression / invoke_dsc_function and updates the expected tool list.
dsc/src/server/invoke_dsc_expression.rs	Implements the new invoke_dsc_expression tool.
dsc/src/server/invoke_dsc_function.rs	Implements the new invoke_dsc_function tool.
dsc/src/server/mcp_server.rs	Registers the new tool routers and updates server instructions i18n key.
dsc/src/server/mod.rs	Exposes the new server modules and updates i18n key usage.
dsc/src/server/invoke_dsc_config.rs	Updates i18n keys from mcp.* to server.*.
dsc/src/server/invoke_dsc_resource.rs	Updates i18n keys from mcp.* to server.*.
dsc/src/server/list_dsc_functions.rs	Updates i18n keys from mcp.* to server.*.
dsc/src/server/list_dsc_resources.rs	Updates i18n keys from mcp.* to server.*.
dsc/src/server/show_dsc_resource.rs	Updates i18n keys from mcp.* to server.*.
dsc/locales/en-us.toml	Moves server-mode strings under [server.*] and adds strings for the new tools.