Add cast kinds

[sim642]

Closes #179.

TODO

• Figure out remaining ~kind:Unknown-s? I don't know what they should be, so maybe just leave for now. The Unknown kind will probably get used in Goblint as well.

[Copilot]

Pull request overview

This PR adds a new castkind type to CIL's AST to distinguish between different types of cast operations. The CastE expression constructor is updated from CastE(typ, exp) to CastE(castkind, typ, exp), allowing the AST to preserve information about why a cast was inserted (e.g., explicit cast, integer promotion, arithmetic conversion, etc.). This addresses issue #179.

Key changes:

• Introduces a new castkind type with 9 variants: Explicit, IntegerPromotion, DefaultArgumentPromotion, ArithmeticConversion, ConditionalConversion, PointerConversion, Implicit, Internal, and Unknown
• Updates all CastE pattern matches and constructor calls throughout the codebase to include the cast kind parameter
• Modifies mkCast and mkCastT functions to require a ~kind parameter, ensuring cast kinds are specified at all call sites

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/cil.mli	Defines the new castkind type and updates CastE, mkCast, mkCastT signatures
src/cil.ml	Implements castkind type, updates CastE handling in all expression functions, adds d_castkind pretty-printer
src/frontc/cabs2cil.ml	Updates all cast operations to use appropriate cast kinds (Explicit, IntegerPromotion, ArithmeticConversion, etc.)
src/mergecil.ml	Updates CastE pattern matches in equality checking to accommodate new parameter
src/expcompare.ml	Updates expression comparison to include cast kind in equality checks, updates cast stripping functions
src/check.ml	Updates type checking for CastE with TODO for validating cast kinds
src/formatparse.mly	Updates parser to use Explicit kind for user casts, Unknown for internal casts
src/formatcil.ml	Updates test code to include Unknown cast kind
src/ext/pta/ptranal.ml	Updates pointer analysis to handle new CastE structure
src/ext/dataslicing/dataslicing.ml	Updates data slicing to preserve cast kinds
src/ext/zrapp/rmciltmps.ml	Updates temporary removal to use Unknown cast kind

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