Mwalib

* mwalib now providews support for Linux/Arm64 platform in releases (and tests).

* Updated pyo3, pyo3-stub-gen, numpy and ndarray.

* Revert to published version of pyo3-stub-gen (and derive) to allow publish to crates.io.

* Ensure only one version of pyo3-stub-gen-derive is used in the project.

* mwalib now will detect and raise an error (`MwalibError::Fits.CfitsioIsNotReentrant`) if the CFITSIO library that mwalib is linked with has been built without the `-D_REENTRANT` directive (github issue 82).
* Expose the FITS BSCALE in image HDUs as a single value `bscale` in `CorrelatorContext` (github issue 85).
* For most Legacy MWA observations, this may be a value other than 1.0. For MWAX correlator this will always be 1.0.
* This is mainly of interest to EoR researchers who are trying to implement Van Vleck corrections.
* Python type stubs:
* Fixed pyo3 decorators to allow stub_gen to work properly / generate python stubs correctly.
* Used prerelease version of pyo3_stub_gen to ensure Chrono::FixedTimeOffset can have a stub generated in `MetafitsContext`.

* Update to fitsio 0.21.6 - provides FitsFile.file_path() method.
* Reverted MWAFitsFile to FitsFile as the subclass is no longer required.