Fix 131k context ggml assert

[createthis]

Just a draft PR for my own personal use. I'm terrible at C++, so no one should trust this. Upstream card is #15049

What?

This PR adds GGML_CUDA_ALLOW_LARGE_TENSORS. When enabled, it allows 64 bit sizes in the CUDA copy routines.

Q. What is the difference in INT_MAX and SIZE_MAX / 4? How much larger of a tensor will this accomodate?

A. The difference between INT_MAX and SIZE_MAX/4 is enormous:

INT_MAX: 2,147,483,647 bytes ≈ 2.00 GB
SIZE_MAX/4: 4,611,686,018,427,387,903 bytes ≈ 4,294,967,296 GB ≈ 4.3 PB

How?

cmake -B build -DGGML_CUDA=ON -DGGML_CUDA_FA_ALL_QUANTS=ON
cmake --build build --config Release

Then:

./build/bin/llama-server \
    --model /data/Qwen3-Coder-480B-A35B-Instruct-1M-GGUF/UD-Q4_K_XL/Qwen3-Coder-480B-A35B-Instruct-1M-UD-Q4_K_XL-00001-of-00006.gguf \
    --alias Qwen3-Coder-480B-A35B-Instruct-GGUF:UD-Q4_K_XL \
    --no-webui \
    --numa numactl \
    --threads 32 \
    --ctx-size 400000 \
    --n-gpu-layers 63 \
    -ot "blk\.(3|4|5|6|7|8|9|10|11|12|13)\.ffn_.*=CUDA0" \
    -ot exps=CPU \
    -ub 4096 -b 4096 \
    --cache-type-k q4_1 \
    --cache-type-v q4_1 \
    --seed 3407 \
    --prio 3 \
    --temp 0.7 \
    --top-p 0.8 \
    --top-k 20 \
    --repeat-penalty 1.05 \
    --min-p 0.0 \
    --log-colors \
    --flash-attn \
    --host 0.0.0.0 \
    --jinja \
    --port 11434

Why?

Cards with a lot of VRAM like the blackwell 6000 pro may enable us to use larger in-GPU context lengths than INT_MAX allows.

[createthis]

Closing in favor of ggml-org#15298