feat: add Godot gdscript language server support via built-in TCP adapter

[K0d1ax]

Summary

This PR adds first-class gdscript support to Serena/SolidLSP.

It introduces a built-in GDScript language server adapter that connects to Godot’s LSP endpoint over TCP (default 127.0.0.1:6005) via an
internal transport process, so users can configure gdscript directly in project.yml.

Important

Godot editor MUST be running with LSP enabled and reachable at configured host/port!

Motivation

Today, gdscript is not a valid Serena language key, so .gd files cannot be handled by symbolic tools through the LSP backend.

Changes

• Added Language.GDSCRIPT = "gdscript" in ls_config.py.
• Added .gd file matching in get_source_fn_matcher.
• Added LS class mapping for gdscript in get_ls_class.
• Added new server implementation:
  • src/solidlsp/language_servers/gdscript_language_server.py
• Added internal stdio<->TCP transport module:
  • src/solidlsp/language_servers/gdscript_tcp_proxy.py
• Updated templates/docs:
  • src/serena/resources/project.template.yml
  • docs/01-about/020_programming-languages.md
  • docs/02-usage/050_configuration.md
  • README.md
  • CHANGELOG.md
• Added tests:
  • test/solidlsp/gdscript/test_gdscript_support.py

Configuration

project.yml:

languages:
  - gdscript

serena_config.yml (optional):

ls_specific_settings:
  gdscript:
    host: "127.0.0.1"
    port: 6005
    connect_timeout: 10.0

## Validation

- uv run --with pytest pytest -o addopts="" test/solidlsp/gdscript/test_gdscript_support.py -q
    - Result: 8 passed
- uv run --with ruff ruff check src/solidlsp/ls_config.py src/solidlsp/language_servers/gdscript_language_server.py src/solidlsp/
  language_servers/gdscript_tcp_proxy.py test/solidlsp/gdscript/test_gdscript_support.py
    - Result: all checks passed

## Notes

- Godot editor must be running with LSP enabled and reachable at configured host/port.
- Defaults align with Godot’s common setup (127.0.0.1:6005).

[K0d1ax]

No conflicts with base branch
Changes can be cleanly merged.