fix: Improve hist binning around breakpoints

[lukemanley]

Improves binning accuracy around breakpoints. Also seems to be 20-30% faster.

import polars as pl

pl.Series([1, 2, 3, 4]).hist(bin_count=3)

# main:

# ┌────────────┬──────────────┬───────┐
# │ breakpoint ┆ category     ┆ count │
# │ ---        ┆ ---          ┆ ---   │
# │ f64        ┆ cat          ┆ u32   │
# ╞════════════╪══════════════╪═══════╡
# │ 2.0        ┆ (0.997, 2.0] ┆ 1     │
# │ 3.0        ┆ (2.0, 3.0]   ┆ 1     │
# │ 4.0        ┆ (3.0, 4.0]   ┆ 2     │
# └────────────┴──────────────┴───────┘

# PR:

# ┌────────────┬──────────────┬───────┐
# │ breakpoint ┆ category     ┆ count │
# │ ---        ┆ ---          ┆ ---   │
# │ f64        ┆ cat          ┆ u32   │
# ╞════════════╪══════════════╪═══════╡
# │ 2.0        ┆ (0.997, 2.0] ┆ 2     │
# │ 3.0        ┆ (2.0, 3.0]   ┆ 1     │
# │ 4.0        ┆ (3.0, 4.0]   ┆ 1     │
# └────────────┴──────────────┴───────┘

[ritchie46]

Nice!