feat(parser): add multiple assignment parsing to arg instruction

[coffeemakingtoaster]

Closes #1

[Copilot]

Pull Request Overview

This PR introduces parsing support for multiple assignment in the ARG instruction by refactoring the parser to populate a key-value map and updating reconstruction and tests accordingly.

• Changed ARG instruction representation from single name/value fields to a map of key-value pairs.
• Updated tests to validate the new output format and adjusted reconstruction logic using strings.Builder for consistency.
• Updated the AST definition to reflect the new ARG instruction structure.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
pkg/parser/parser_test.go	Updated test comparisons to validate the new key-value map.
pkg/parser/parser.go	Modified parsing function to support multiple assignments.
pkg/ast/reconstruct_test.go	Revised tests to reflect the changed format in reconstructed ARG.
pkg/ast/reconstruct.go	Refactored ARG reconstruction using sorted keys and strings.Builder.
pkg/ast/ast.go	Updated AST definition for ARG to use a key-value map and modified ToString.