Optimise floating point/SIMD context-save/restore

Currently, the hyperlight_guest exception handlers are compiled along with the rest of the guest code, and the compiler sometimes introduces floating point/SIMD instructions (e.g. exception handlers use the same memcpy as the rest of the guest, which uses XMM registers on x86-64). Because of this, we currently save and restore the entire floating point and SSE register state on every context switch (see [here](https://github.com/hyperlight-dev/hyperlight/blob/ea6fa8f16dae2325d94af39eb6ac3b441b24dcac/src/hyperlight_guest_bin/src/exceptions/interrupt_entry.rs#L74). This is not ideal, because it makes the context-save large and slow.

Other kernels, like Linux, arrange for most kernel code to be compiled without FPU/SIMD, and in the few cases where it's a good performance tradeoff to use SIMD in the kernel at the cost of the extra overhead, they have `kernel_fpu_begin()`/`kernel_fpu_end()`. We should figure out a way to compile Hyperlight in a similar configuration, and see if it's a performance improvement to do so.