Pod5

Fixed

- Fixed merging many files running out the size limit of dictionary indices.

Changed

- `pod5 convert fast5` now creates logs when `POD5_DEBUG=1` set
- `pod5 convert fast5` checks multi-read fast5s at conversion time

Fixed

- Fixed memory usage growth over time as signal was loaded with large pod5 files.
- Fixed crash loading malicious files (found via fuzz testing)
- Fixed leaks and UB when running unit tests.
- Fixed run-away memory consumption during fast5 conversion

Changed

- Updated internal arrow version to 8.0.0.3

Fixed

- Fixed issue where pod5 would read out of bounds memory when decompressing some reads.

Changed

- Refactored `pod5 convert fast5` to use `concurrent.futures` only.
- Add further info to error message when signal cannot be decompressed by zstd
- Make merge operation not generate multiple identical run infos.

Fixed

- Fixed closing uninitialised file handles.
- Fixed `pod5 inspect reads` repeating header
- Fixed a crash with certain pod5 search operations.

Fixed

- Fix loading large pod5 files on virtual-memory limited systems.