[Feat] support composite type based on DslType

[sjfeng1999]

Motivation

Technical Details

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[Copilot]

Pull request overview

This PR introduces a unified “composite type” layer for FlyDSL (struct/union/align/array/storage) built on top of existing DSL type protocols, and updates the compiler’s constexpr handling to work with the new Constexpr type model.

Changes:

• Adds a new composite schema system (@struct, @union, inline schema syntax), plus Align[...] and Storage[...] for layout-aware memory views.
• Reworks Constexpr from a typing-only generic into a runtime-specializable type, and updates JIT/kernel pipelines to detect constexpr annotations via Constexpr.is_constexpr_annotation.
• Introduces an Array[dtype, size, (align)] composite/storable type and expands numeric types to implement the Storable protocol where applicable.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/unit/test_struct.py	New unit coverage for struct/union/constexpr/layout/align/storage and Array behavior.
python/flydsl/expr/typing.py	Implements runtime Constexpr, adds Array, and adds Pointer.view(...).
python/flydsl/expr/struct.py	New composite schema implementation, layout computation, Align, and Storage.
python/flydsl/expr/numeric.py	Adds Storable protocol support (size/align/peek/poke) for storable numerics and adds Numeric.__coerce__.
python/flydsl/expr/init.py	Re-exports the new struct module symbols.
python/flydsl/compiler/protocol.py	Adds Storable protocol + dsl_size_of/dsl_align_of/peek_from_ptr/poke_into_ptr helpers.
python/flydsl/compiler/kernel_function.py	Switches constexpr detection to Constexpr.is_constexpr_annotation.
python/flydsl/compiler/jit_function.py	Switches constexpr detection to Constexpr.is_constexpr_annotation and imports is_type_param_annotation.
python/flydsl/compiler/jit_argument.py	Removes old constexpr helper and renames _is_type_param_annotation to is_type_param_annotation.

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