Ptufile

- Rename PqFileMagic to PqFileType (breaking).
- Rename PqFile.magic to PqFile.type (breaking).
- Add PQDAT and SPQR file types.

- Add options to specify file open modes to PqFile and PtuFile.read_records.
- Add convenience properties to PqFile and PtuFile.
- Cache records read from file.

- Fall back to file size if TTResult_NumberOfRecords is zero (2).

- Add imwrite function to encode TCSPC image histogram in T3 PTU format.
- Add enums for more PTU tag values.
- Add PqFile.datetime property.
- Read TDateTime tag as datetime instead of struct_time (breaking).
- Rename PtuFile.type property to record_type (breaking).
- Fix reading PHU missing HistResDscr_HWBaseResolution tag.
- Warn if tags are not 8-byte aligned in file.

- Support bi-directional sinusoidal scanning (WIP).

- Support bi-directional scanning (FLIMbee scanner).
- Drop support for Python 3.9.