b9908

server: enforce prompt cache RAM limit (#25070)

Before this commit, --cache-ram was not a hard limit:

• The cache always kept at least one entry, even if that entry exceeded the
  RAM/token limits.
• Old entries were only evicted for the RAM/token limits after saving the new
  one, which could cause the cache to temporarily exceed the RAM/token limits
  even if individual entries were below the limit.

Now, ensure that the RAM limit is strict with these changes:

• Skip saving state to cache if by itself it exceeds the RAM limit.
• Evict old entries as necessary to make the new entry fit.

Additionally, token-limit cleanup may now evict the last remaining cache entry
instead of always preserving one.

macOS/iOS:

• macOS Apple Silicon (arm64)
• macOS Apple Silicon (arm64, KleidiAI enabled) DISABLED
• macOS Intel (x64)
• iOS XCFramework

Linux:

• Ubuntu x64 (CPU)
• Ubuntu arm64 (CPU)
• Ubuntu s390x (CPU)
• Ubuntu x64 (Vulkan)
• Ubuntu arm64 (Vulkan)
• Ubuntu x64 (ROCm 7.2)
• Ubuntu x64 (OpenVINO)
• Ubuntu x64 (SYCL FP32)
• Ubuntu x64 (SYCL FP16)

Android:

• Android arm64 (CPU)

Windows:

• Windows x64 (CPU)
• Windows arm64 (CPU)
• Windows arm64 (OpenCL Adreno)
• Windows x64 (CUDA 12) - CUDA 12.4 DLLs
• Windows x64 (CUDA 13) - CUDA 13.3 DLLs
• Windows x64 (Vulkan)
• Windows x64 (OpenVINO)
• Windows x64 (SYCL)
• Windows x64 (HIP)

openEuler:

• DISABLED
• openEuler x86 (310p)
• openEuler x86 (910b, ACL Graph)
• openEuler aarch64 (310p)
• openEuler aarch64 (910b, ACL Graph)

UI:

• UI