C: Implement merging arena pages

[timkaechele]

Based on the arena pages proposed in #708 by @marcoroth, this PR builds on the concept and adds a more refined reset behavior that merges obsolete pages into one big page.

This has the advantage that we won't have a bunch of small pages, and instead have more contiguous memory available.

How it works

# Initial state
| Page 1 (4kb) | - next > | Page 2 (4kb) | - next > | Page 1 (16kb) | 

# reset to  4kb
| Page 1 (4kb) | - next > | Page 2 (24kb) |

# reset to 0kb
| Page 1 (4kb) | - next > | Page 2 (24kb) |

For now the first page is never deallocated and merged into a bigger page for two reasons:

1. It's an edge case that needs to be handled.
2. If the allocation of a new arena page fails at least you still have the first page. 🤷‍♂️

Related: #1155