rocm714 variants parse as rocm 71.4 #995

the legacy rocm regex rocm(\d+)(\d+) in backends.py splits flattened versions before the last digit, so rocm714 parses as 71.4 instead of 7.14 and torch*-rocm714 variants are rejected on a rocm 7.14 system

python -c "import re; m = re.fullmatch(r'rocm(\d+)(\d+)', 'rocm714'); print(m[1], m[2])"

71 4

hit this in the kernels-community rocm ci where every kernel fails with Cannot find a build variant for this system

note: the error has no rejection reasons since resolve_local_kernel overwrites trace with the repo_path / "build" pass, which finds no variants, so the rocm version rejection from the first pass is lost