feat: basic BoolBuffer / BoolBufferMut

[a10y]

It's very annoying to do random in-place setting of bits in Arrow BooleanBufferBuilder. It's very append focused. For something like SparseArray in particular, you want to create a BoolArray against uninitialized memory and only set the bits corresponding to positions of non-null values.

[gatesn]

Can we call this BitBuffer?

[gatesn]

Think we'll also want iterators and vectorized constructors (i.e. BooleanBuffer::collect_bool)

[gatesn]

Do we want to guarantee that we only hold a bit_offset? i.e. offset < 8?

[a10y]

Hmm, does that help much?

[a10y]

Sadly new_uninit leads to UB when you try and do inplace updates on it. I can't think of a great way to work around that without doing something like having a second bitset, which sort of defeats the point of avoiding the initialization cost anyway, so for now I'm just removing it.

[gatesn]

Where are we at with this? Need someone to takeover while you poke at FFI bindings?

[a10y]

Maybe? I'm no longer sure there's a strong path forward that gives us something better than Arrow's BooleanBufferBuilder.

The big issue is that mapping a bitset on top of uninit memory causes UB when you try and set bits in-place. While it generally seems harmless it is technically a violation of Rust's memory model so not guaranteed to work across platforms.

[gatesn]

Why does the memory have to be uninitialized? Even the ability to into_mut and update bits is valuable from an API perspective.

[robert3005]

I will take over this pr