Small improvements

[Intuity]

A number of small improvements:

• Flags unused or invalid constant overrides when parsing packtype grammar
• Constant expressions can be optionally attached as _PT_EXPRESSION if keep_expression=True when using packtype grammar (utils.constant.get_expression() can be used to retrieve this)
• Addition of __float__ and __index__ methods to NumericPrimitive to reduce the need for explicit int(...) casts in many places

[Copilot]

Pull Request Overview

This PR adds several small improvements to the packtype library including better constant override validation, optional expression preservation for constants, and enhanced numeric primitive methods.

• Adds validation to flag unused or invalid constant overrides when parsing packtype grammar
• Enables optional preservation of constant expressions as _PT_EXPRESSION attribute when keep_expression=True
• Adds __float__ and __index__ methods to NumericPrimitive to reduce explicit casting needs

Reviewed Changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
packtype/grammar/grammar.py	Adds validation for constant overrides and expression preservation logic
packtype/types/constant.py	Adds _PT_EXPRESSION attribute to store parsed expressions
packtype/types/numeric.py	Adds __index__ method for numeric primitives
packtype/types/primitive.py	Adds __float__ method for primitive types
packtype/utils/constant.py	New utility module for constant-related operations
packtype/common/expression.py	Refactors expression classes with improved naming and documentation
tests/	Various test files covering new functionality
examples/structs/spec.pt	Updates example to use constants for field widths