feat(language-server): add python variable line for robot goto

[leojuurinen-vala]

Add parsing of the variables from python files to include their line for navigation from robot.

Root Cause: Python variables imported from .py files had hardcoded line_no=1, col_offset=0, causing go-to-definition to always jump to the beginning of the file instead of the actual variable definition line.

Solution: Added AST-based line number extraction that parses Python source files to find the actual line numbers and column offsets where variables are defined. Support for RF >= 7.0.