Refactorings for TPC-H and span-based data structures

[phoeinx]

Tracking issue for everything that needs to be adapted to allow for a clean(-ish) mmap-based TPC-H run:

Functional

• [TPC-H 09]: Doesn't run through due to issue in for-based range loop over dictionary -> FixedStringSpanIterator seems to have a bug.
• [TPC-H 11]: Somehow only works when run once, not when run twice?

Major

• [Byte* Map]: We currently store our map as a uint32_t* (due to legacy reasons). This means that we can only access it in four-byte steps, making padding every written section to four byte divisible byte lengths necessary. It should be possible and easier to store the map as a byte* and cast as necessary.

Formschön

• [Stream instead of Filename]: Make things pretty like in BinaryWriter and don't pass file_name but a file_stream.