Unify surrogate/no-surrogate mapping behind a single abstraction

[danbugs]

Context

PR #1578 adds a no-surrogate mode (HYPERLIGHT_MAX_SURROGATES=0) that uses WHvMapGpaRange instead of WHvMapGpaRange2. Currently whp.rs branches on Option<SurrogateProcess> to choose the mapping path.

Proposal

Unify the surrogate and no-surrogate paths so whp.rs doesn't need to know or care which mode is active. Two possible approaches:

1. Enum / trait abstraction: Make SurrogateProcess an enum (or dyn Trait) with two variants — one backed by a real surrogate process (WHvMapGpaRange2) and one that maps from the host process directly (WHvMapGpaRange). The NoSurrogateGuard could be folded into the no-surrogate variant.

2. Always use WHvMapGpaRange2: Use the current process handle as the source when surrogates are disabled, eliminating the branch entirely. This needs validation — it's unclear whether WHvMapGpaRange2 with GetCurrentProcess() is a supported pattern.

Either way, the mapping call would move into the surrogate module so whp.rs just calls a single map(...) method.

Origin

Suggestion from @syntactically in PR #1578 review.