Fix bst

[misdake]

fix bst:

• fix compute_sub_space: fix subspace size, reuse numbers to fix f32 precision loss (fix https://github.com/mikialex/rendiation/issues/98)
• fix build: copy bounds before child resets builder
• fix build: fix child indices for visit_children
• fix apply_index_source: save crossed children at the start of parent range (Is this the approach you intend to take?)
• test: print tree in test.rs (including "crossed" children), check for duplicates in sorted_primitive_index
• test: use rand_chacha for reproducible test
• test tree

[mikialex]

is this pr also fix #97 ?

crossed children was overridden and ignored, that clearly a mistake. I think this fix is ok!