ggml : split graph allocations according to backend max buffer size (#15815)

* ggml : make gallocr respect the backend's max buffer size

* if the graph requires more memory than can fit into a single allocation, split it into multiple backend buffers
* vulkan: report the actual max  allocation size in buffer type  interface

* fix missing newline, apple-clang warning

* track size of individual chunks in ggml_dyn_tallocr and raise max chunks.
revert to use suballocation_block_size as max chunk size for vulkan.

* track (chunk, offset) pairs instead of "global" offsets through gallocr.

* simpler, don't need loops to map between local/global offsets
* touches more code

* fix dyn_tallocr_max_size and initialization

* fix memory leak when buffers are reused due to same buffer type appearing multiple times

* make vbuffer allocation follow the same logic as backend_buffer did before

* continue to use leftover unallocated space of previous chunks after a new one has been created

* treat free blocks of each chunk as separate list
* they're still allocated together, but start/end of each chunk is tracked, and allocate/free iterate over sub-ranges
* exhaust freed blocks of all chunks before considering their last blocks with unallocated space
* start with 0 chunks/blocks and create chunks as needed
* allow the last chunk to grow beyond max size

* refactor: move adding new free block and new chunk into separate functions

* allocate chunks individually with a separate free-blocks list for each one

* needs a bit more memory/allocations/indirections, but code is simpler

* fix warnings (missing static) & debug checks

tests/CMakeLists.txt

@@ -219,3 +219,6 @@ target_link_libraries(${LLAMA_TEST_NAME} PRIVATE mtmd)
 get_filename_component(TEST_TARGET test-c.c NAME_WE)
 add_executable(${TEST_TARGET} test-c.c)
 target_link_libraries(${TEST_TARGET} PRIVATE llama)
+
+llama_build_and_test(test-alloc.cpp)
+target_include_directories(test-alloc PRIVATE ${PROJECT_SOURCE_DIR}/ggml/src)