Require AllocCheck 0.2 in StochasticDiffEq tests

[ChrisRackauckas-Claude]

Ignore this PR until it has been reviewed by @ChrisRackauckas.

Summary

• require AllocCheck 0.2 for the StochasticDiffEq test target
• bump StochasticDiffEq to 7.1.4

Clean-master failure

Commit 07d93a606d added AllocCheck as a test extra without a compatibility floor. The sublibrary downgrade action therefore selects AllocCheck 0.1.0 together with GPUCompiler 0.24.5 and LLVM 6.6.3. On Julia 1.12, that stack fails while precompiling AllocCheck with:

InitError: type Nothing has no field major

The error originates in GPUCompiler 0.24.5 before any StochasticDiffEq tests can run.

Local verification

I reproduced the exact mutable downgrade action at 30b83cf94e89744fcbd7ea5496be4967d6fbe540 on untouched master a7080c6f6d:

• without this compat floor: resolver selects AllocCheck 0.1.0 / GPUCompiler 0.24.5 / LLVM 6.6.3, and GROUP=Core exits during AllocCheck precompilation
• with this branch's exact Project.toml change: resolver selects AllocCheck 0.2.0 / GPUCompiler 0.27.8 / LLVM 9.11.0, and the full official Core group passes, including solver-reversal 152/152
• git diff --check passes