GH-5686 LMDB page walking estimator

[hmottestad]

GitHub issue resolved: #

Briefly describe the changes proposed in this PR:

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• I've added tests for the changes I made
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[hmottestad]

@kenwenzel want to take a look?

Test results are promising, benchmarks too.

Some of the benchmarks do show some regressions, but I'm wondering if maybe it's just that the previous plan was faster specifically because the estimated cardinalities were inaccurate.

[kenwenzel]

@hmottestad Does it make sense to completely port LMDB to Java? I see that your code already mirrors many of LMDB's internals.