A10 - Add ESCAPED_IDENTIFIER token to support backtick escaping

[ruizmaa]

closes #53

Summary

Adds backtick escaping so DPM-XL reserved words can be used as property names, temporary identifiers, and key names

• Adds ESCAPED_IDENTIFIER lexer token in three modes: default, CLAUSE_MODE, and GROUPING_CLAUSE_MODE
• Extends parser rules propertyCode, temporaryIdentifier, and keyNames to accept ESCAPED_IDENTIFIER
• Strips backticks in the AST constructor so the resulting node is identical to the unescaped form
• Regenerates all ANTLR parser files from the updated .g4 sources

Tests

New test file tests/unit/ast/test_escaped_identifier.py:

• Valid forms across all three contexts are accepted
• Backtick stripping produces the correct node
• Malformed backtick expressions are rejected

Checklist

• Code quality checks pass (ruff format, ruff check, mypy)
• Tests pass (pytest) with 100% branch coverage (coverage report --fail-under=100)
• Documentation updated (if applicable)

Impact / Risk

• Breaking changes? (public API / CLI / REST endpoints / Django models)
• Database schema or migration concerns?
• Notes for release/changelog?

Notes

[javihern98]

Looks good, thanks! 😊