Increase max nodes per page.

## Overview

This commit effectively removes the `maxNodesPerPage` constant so that it is essentially unlimited. Previously, a single large transaction could create more nodes than the mock array could handle which would cause a panic.

## Notes

The `maxNodesPerPage` previously existed with a value of 64K because a page's inode count is limited by the range of a `uint16`. However, this doesn't account for the fact that nodes could grow larger than this during a large transaction and then would be split before being written to disk.

Fixes #188.

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/cc @PreetamJinka @snormore @mkobetic