feat(libkernel): hinted and no-overwrite mappings, virtual range names and usleep
- **Non-fixed mapping with an address hint:** `MapAligned` threw `Non-fixed mapping address hints are not implemented`. On the PS5 the hint is where the search starts. On Linux the mapping is now placed at the first free, aligned range at or above the hint, found from `/proc/self/maps` and mapped with `MAP_FIXED_NOREPLACE` so nothing existing can be replaced. `RequireAvailable` is now only checked for fixed mappings, because a hint may point at used memory. Windows still throws.
- **`SCE_KERNEL_MAP_NO_OVERWRITE` (`0x80`):** it was rejected as an unknown flag. With `MAP_FIXED` on Linux it maps with `MAP_FIXED_NOREPLACE`, and it no longer takes the "remap fixed into registered" path, so it fails instead of replacing a registered range. The unsupported-flags error now includes the flag value.
- **Virtual range names:** `sceKernelSetVirtualRangeName` was `NotImplemented` and `sceKernelClearVirtualRangeName` wasn't exported. Names are now kept in a registry, split and trimmed on overlap. `sceKernelVirtualQuery` reports the name and splits its reported region at name boundaries. `sceKernelMapNamedDirectMemory` and `sceKernelMapNamedFlexibleMemory` now name the range instead of ignoring the name.
- **`usleep`** is exported (POSIX, beside `nanosleep`).
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