Sample Project for INCF- Comment Support

[Cairo09]

Changes made:

1. Added description and inline_comments parameters to Variable.init and stored them as instance attributes with list conversion for comments.
2. Propagated these parameters through ArrayVariable.init, Subexpression.init, Variables.add_array(), and Variables.add_subexpression()
3. Replaced Combine-based expression parsing with FRAGMENT groups capturing text/comments separately
4. added DESCRIPTION token to all equation types; rewrote fragment processing to extract inline_comments with parenthesis stripping
5. updated SingleEquation to store metadata
6. Passed description and inline_comments from equations to variables.add_array() and add_subexpression().

Added tests:

1. which verifies parsing of inline comments and descriptions
2. which verifies that NeuronGroup variables receive description and inline_comments

All tests passed