feat[next]: Add support for tuple comprehensions (not stacked)

[SF-N]

Adds support for tuple comprehensions, e.g. for usage on tracers.

@gtx.field_operator
def testee(
    tracers: tuple[cases.IField, cases.IField], factor: int32
) -> tuple[cases.IField, cases.IField]:
    return tuple(tracer * factor for tracer in tracers)

[tehrengruber]

This is for direct access to tracers[0] * factor, tracers[1] * factor, which I personally think is an anti pattern. I left it here until we take a decision on this. We could also make it an optional feature. One of the disadvantages is that it is not possible to fully type check the field operator at definition time, since the tuple length is only known at call / compile time. The user will then get an error in unroll_map_tuple.

[Copilot]

Pull request overview

This PR adds frontend + lowering support for tuple comprehensions written as tuple(<genexpr>), enabling mapped operations over tuple-typed inputs (including variadic tuple annotations) and lowering them through a new iterator builtin (map_tuple) that is later unrolled into explicit tuple element operations.

Changes:

• Parse tuple(<generator expression>) into a dedicated FOAST node and pretty-print it.
• Type-deduce tuple comprehensions (incl. variadic tuple annotations via VarArgType) and lower them to iterator IR using a new map_tuple builtin.
• Add an iterator transform to unroll map_tuple calls, plus integration/unit tests for supported and unsupported cases.

Reviewed changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
tests/next_tests/unit_tests/ffront_tests/test_func_to_foast.py	Adds negative tests for invalid tuple-comprehension forms.
tests/next_tests/integration_tests/feature_tests/ffront_tests/test_execution.py	Adds execution tests covering fixed/variadic/nested tuple comprehensions.
tests/next_tests/integration_tests/cases.py	Adds temporary allocation/size handling for VarArgType (currently fixed to length 3).
src/gt4py/next/type_system/type_translation.py	Adds variadic/generic tuple hint handling and tuple constructor typing.
src/gt4py/next/type_system/type_specifications.py	Introduces VarArgType to represent variadic tuples.
src/gt4py/next/type_system/type_info.py	Extends concretization logic to account for VarArgType.
src/gt4py/next/iterator/type_system/type_synthesizer.py	Adds type synthesizer for new map_tuple builtin.
src/gt4py/next/iterator/transforms/unroll_map_tuple.py	New transform to unroll map_tuple into explicit tuple construction.
src/gt4py/next/iterator/transforms/pass_manager.py	Wires UnrollMapTuple into iterator transform pipelines.
src/gt4py/next/iterator/builtins.py	Registers map_tuple as an iterator builtin.
src/gt4py/next/ffront/past_passes/type_deduction.py	Relaxes out= typing check to compatible types.
src/gt4py/next/ffront/func_to_foast.py	Parses tuple(genexpr) into FOAST TupleComprehension.
src/gt4py/next/ffront/foast_to_past.py	Uses concretizability check for out return type validation.
src/gt4py/next/ffront/foast_to_gtir.py	Lowers tuple comprehensions to map_tuple(lambda)(iterable) calls, incl. unpacking targets.
src/gt4py/next/ffront/foast_pretty_printer.py	Adds pretty-print support for tuple comprehensions.
src/gt4py/next/ffront/foast_passes/type_deduction.py	Adds typing rules for TupleComprehension and vararg tuple indexing behavior.
src/gt4py/next/ffront/field_operator_ast.py	Adds FOAST node types for tuple comprehensions and mapper structure.

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[SF-N]

Continued in stacked PR #2833