ffi: expose array validity, allow creating primitive arrays

[myrrc]

• Allow querying array validity from FFI.
• Allow creating null and primitive vx_arrays from FFI.
• Expose utility functions to query dtype and ptype from array
  directly instead of array -> dtype -> variant [-> ptype] chain
  Breaking changes:
• rename vx_array_element_is_null from vx_array_is_null
• rename vx_array_null_count to vx_array_invalid_count.

[codspeed-hq]

Merging this PR will degrade performance by 15.51%

❌ 3 regressed benchmarks
✅ 1098 untouched benchmarks
⏩ 1522 skipped benchmarks¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	bitwise_not_vortex_buffer_mut[1024]	477.2 ns	535.6 ns	-10.89%
❌	Simulation	bitwise_not_vortex_buffer_mut[128]	317.8 ns	376.1 ns	-15.51%
❌	Simulation	map_each[BufferMut<i32>, 128]	770.6 ns	858.1 ns	-10.2%

---

_{Comparing myrrc/primitive-ffi (a3c15ad) with develop (0ea8973)}

Footnotes

1. 1522 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[0ax1]

This wasn't introduced as a pattern in this PR, but we should consider documenting in the code what C-unwind implies / allows for (compared to extern "C"), explaining how the unwinding can be leveraged.

[0ax1]

The ptr parameter name should be more descriptive. Shall we have in the fn docs describing what each param is for, here and elsewhere?

[0ax1]

Should they have different fn name prefixes? They kinda do different things no?

[myrrc]

They both extract a view of the error string messsage, so they do the same thing

[0ax1]

In impl From<&vx_validity> for Validity, we clone the arc validity::Array(vx_array::as_ref(value.array).clone()) (aka atomic ref counted pointer).

Saying we don't take ownership of validity as mentioned in the new_primitive docs.

[0ax1]

We need to double check the consistency of size types for indices:

vx_array_get_field` | `uint32_t` |
| `vx_array_slice` | `uint32_t` |
| `vx_array_get_u8` etc. | `uint32_t` |
| `vx_array_null_count` return | `uint32_t

should prob all be size_t.