ZJIT: Narrow `type InlineDepth = usize`

[alanwu-shopify-inc]

ruby#18293 found that usize is too big for InlineDepth, as narrowing it at runtime is combersome and not particularly useful. We should cap it at command line parsing time.

[tekknolagi]

Let's make it a u8 then

[alanwu-shopify-inc]

A bit more context: base_ptr_slot_native_base_ptr_offset and base_ptr_slot_index in ruby@c81bc76 bounds jit_frame_size to i32 by doing a runtime check with possibility to panic. The size itself is bound by how many frames deep we inline. Realistically we wouldn't inline i32::MAX levels deep, anyways, but there's --zjit-inline-max-iterations allowing users to tweak the maximum. We can remove the panic possibility and simplify the code a little bit by putting a hard limit on the inline depth.