Add allocation regression tests for core FVM functions

[ChrisRackauckas-Claude]

Summary

• Added allocation regression tests to ensure the core computational hotpath remains allocation-free
• Verified that the package is already well-optimized with excellent performance

Benchmarking Results

The benchmarking analysis showed that:

• serial_fvm_eqs! is completely allocation-free for both FVMProblem and FVMSystem
• get_triangle_contributions!, get_boundary_edge_contributions!, and get_source_contributions! are all allocation-free
• The parallel path has minimal allocations (~8KB for FVMProblem, ~27KB for FVMSystem) which are from Julia's threading infrastructure (expected and unavoidable behavior from Threads.@threads)

Benchmark Numbers (611 triangles, 342 vertices)

Function	Time	Allocations
serial_fvm_eqs!	~136 μs	0 bytes
get_triangle_contributions!	~106 μs	0 bytes
get_boundary_edge_contributions!	~16 μs	0 bytes
get_source_contributions!	~12 μs	0 bytes

Individual Function Performance

Function	Time	Allocations
get_shape_function_coefficients	~9 ns	0 bytes
get_fluxes	~5 ns	0 bytes
fvm_eqs_single_triangle!	~28 ns	0 bytes

Changes

1. test/alloc_tests.jl (new file): Allocation regression tests for:

   • FVMProblem serial path functions
   • FVMSystem serial path functions

2. test/runtests.jl: Updated to include allocation tests in the test suite (conditionally based on GROUP env variable for CI flexibility)

Test Plan

• Allocation tests pass locally (7/7 tests)
• Full test suite runs (allocation tests integrated)
• Verified no regressions in existing functionality

Notes

The package is already well-optimized with:

• Type-stable core functions with @inline annotations
• Pre-computed and cached triangle properties
• No heap allocations in the main computation loop

These tests will help prevent future performance regressions.

cc @ChrisRackauckas

🤖 Generated with Claude Code