PERF: IntervalArray.unique, IntervalIndex.intersection

[jbrockmendel]

• closes #xxxx
• tests added / passed
• Ensure all linting tests pass, see here for how to run them
• whatsnew entry

Partially address perf hit discussed in #41929

import numpy as np
from pandas import *

N = 10**5

left = np.append(np.arange(N), np.array(0))
right = np.append(np.arange(1, N + 1), np.array(1))
intv = IntervalIndex.from_arrays(left, right)

intv2 = IntervalIndex.from_arrays(left + 1, right + 1)

%timeit intv.intersection(intv2)
122 ms ± 2.34 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)  # <- PR
263 ms ± 5.98 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)  # <- master

xref #36482

[jreback]

@meeseeksdev backport 1.3.x

[lumberbot-app]

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