docs: refine the documents

[windreamer]

Motivation

This PR aims to systematically improve the documentation quality and maintainability of the LMDeploy project. The existing documentation had inconsistencies in formatting, suboptimal Sphinx configuration, and outdated code examples that hindered readability and API reference generation. Additionally, the lack of proper type hint documentation diminished the developer experience when navigating the codebase.

Modification

This is a comprehensive documentation refinement with three core improvement areas:

1. Sphinx Configuration Modernization
   Reorganized and extended the Sphinx extensions list for better build performance and functionality. Added sphinx-autodoc-typehints for automatic type annotation rendering and configured autodoc_type_aliases to properly handle Pydantic dataclasses, enabling cleaner API documentation generation.

2. Documentation Format Standardization
   Applied consistent capitalization rules across all heading levels in RST files and standardized TOML configuration examples by enforcing quoted string values and lowercase boolean literals. Merged fragmented configuration class documentations into unified sections to improve scannability.

3. API Documentation Enhancement
   Refactored Python docstrings to use proper Sphinx directives (e.g., code-block, inline literals) instead of plain text examples. Updated parameter descriptions to remove redundant type annotations (following Sphinx best practices) and replaced generic returns with specific type hints. This produces more accurate and navigable API references while maintaining backward compatibility.

The changes are purely documentation-focused and do not affect runtime functionality.