ggml-backend update: buffer types, backend registry, graph compare, tests (#620)

ggml-backend update: buffer types, backend registry, graph compare, tests (#620)

* ggml-backend update

* update metal backend

* show metal logs with ggml-backend

* move buffer types to functions

* cuda: add per-device backends

* cuda: add host buffer type

* fix metal build

* ggml_backend_alloc_ctx_tensors : ignore allocated tensors

* ggml_backend_compare_graph_backend fixes

* ci : try to fix metal build

* metal : first print device info, then build kernels

* ci : disable GGML_METAL on Github Actions

* test-backend-ops initial impl (unary and get_rows)

* more op tests

* cleanup

* print test params, add more tests cases for add and mul

* add tests for im2col

* better f16 init

* metal : add basic impl of supports_op

* add test for ggml_concat

* update im2col test params, show callstack with GGML_ASSERT on CUDA failures

* add more rope tests

* add more rope and mul_mat test cases

* add more get_rows test cases
ggml-ci

* add more norm and rms_norm test cases with different eps

* ci : fix metal resource path

ggml-ci

* tests : silence warning

* add ggml_backend_tensor_alloc and ggml_backend_view_init for initializing tensors without ggml-alloc

* add mul_mat test cases without dims 3 and 4
ggml-ci

* check for nans and infs
ggml-ci

* add diag_mask_inf test cases without dims 3 and 4
ggml-ci

* fix cuda leak while backend reg

* fix msvc issues

* remove backend_sched debug causes by default

* gpt-2 : increase graph size

ggml-ci

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Co-authored-by: Georgi Gerganov <redacted>