Support need items generation from marked RST in source code

[juiwenchen]

Addressing #43 by adding simplified RST directive parser and feature to remove leading sequences of marked RST text

Documentation

• Added a dedicated section (docs/source/components/rst_parser.rst) describing the new simplified RST parser, its purpose, and limitations.

RST block extraction and parsing:

• Added a new parser module using Lark to parse extracted RST blocks, extracting directive type, argument, options, and content.
• Updated MarkedRstConfig and related configuration files to support new fields: strip_leading_sequences, indented_spaces, and link_options for more stable RST extraction and parsing.

Integration and warning handling:

• Integrated the RST parser into the extraction workflow in analyse, including logic to handle parsing errors and report warnings.
• Extended the MarkedRst model to store parsed need data from RST blocks.