Simplify BLIS integration to use existing test framework

- Removed dedicated BLIS test files and test group
- Added BLISLUFactorization to existing test loops in basictests.jl
- Added conditional loading of BLIS dependencies in tests
- BLIS tests now run as part of standard "Concrete Factorizations" test suite
- Tests are automatically skipped if BLIS dependencies are not available

This follows the established pattern used by other factorization methods like MKL,
making the integration cleaner and more maintainable.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: ChrisRackauckas

Project.toml

@@ -49,8 +49,8 @@ SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
 Sparspak = "e56a9233-b9d6-4f03-8d0f-1825330902ac"
 
 [extensions]
-LinearSolveBandedMatricesExt = "BandedMatrices"
 LinearSolveBLISExt = ["blis_jll", "LAPACK_jll"]
+LinearSolveBandedMatricesExt = "BandedMatrices"
 LinearSolveBlockDiagonalsExt = "BlockDiagonals"
 LinearSolveCUDAExt = "CUDA"
 LinearSolveCUDSSExt = "CUDSS"