Native raw pointer traversal for NativeType values

[TristonianJones]

Improve performance of CEL's native type handling by supporting raw pointer traversal

Notably, the performance improves considerably:

Feature / Operation	Legacy CEL-Go (Reflection)	Third-Party Fast Adapter	Present CEL-Go (native-rawptr)
Primitive Field Access (msg.Int64Val == 10)	~390 ns / 5 allocs	~100–120 ns / 1–2 allocs	100.4 ns / 1 alloc (16 B)
Pointer Field Access (msg.PtrString == 'val')	~270 ns / 3 allocs	~80–110 ns / 1–2 allocs	61.3 ns / 1 alloc (16 B)
Field Presence Testing (has(msg.Field))	~320 ns / 4 allocs	~160–200 ns / 0–1 allocs	85.6 – 155.5 ns / 0 allocs (0 B)
Nested Struct Access (msg.Nested.Field)	~580 ns / 8 allocs	~140–180 ns / 2–3 allocs	125.2 ns / 2 allocs (32 B)
Nested Struct Presence (has(msg.Nested.Field))	~440 ns / 6 allocs	~200–240 ns / 0–1 allocs	169.9 ns / 0 allocs (0 B)
Comprehension on Slice (msg.Slice.all(...))	~980 ns / 12 allocs	~550–700 ns / 2–4 allocs	495.7 ns / 1 alloc (64 B)