Add JET static analysis and type inference tests

[ChrisRackauckas-Claude]

Summary

• Add JET.jl static analysis tests to verify type stability of core functionality
• Add @inferred tests to verify return type inference
• Add JET as a test dependency with compat bounds

JET Analysis Results

The package was analyzed with JET.jl. Key findings:

Core functionality is type-stable:

• @test_opt passes for all wrapper calls when using the non-fallback mode (FB=false)
• JET.report_call shows no errors for the main code paths
• Return types are correctly inferred

Known type instabilities (by design):

• The fallback path (FB=true) has inherent type instability because it calls the unwrapped function directly via .obj[], which loses type information
• Some runtime dispatch in the constructor is expected when building the tuple of FunctionWrappers from runtime type information
• Some upstream issues exist in FunctionWrappers.jl itself (in reinit_wrapper/gen_fptr), which are not addressable in this package

Test Plan

• All existing tests pass
• New JET static analysis tests pass (7 tests)
• New type inference tests pass (5 tests)

Changes

• Project.toml: Add JET as test dependency with compat entry
• test/runtests.jl: Add JET static analysis and type inference test sets

/cc @ChrisRackauckas

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