Mwalib

* Added calibrator and calibrator_source to `metafits_context`
* Reverted efa8ca41edccbe15079642b26ed5049a8656e3a9 (behaviour of coarse_chan.gpubox_number for VoltageContext LegacyVCS use-case)

* Added new metafits key RAWSCALE to metafits context
* Made gridnum and global_analogue_attenuation_db optional (since they are not in every historical metafits)
* For Legacy VCS, coarse channel.gpuboxnumber now matches the values used by the Legacy Correlator (instead of receiver channel number)
* Added back constants recently removed as they were needed by FFI users: MWALIB_MWA_LATITUDE_RADIANS, MWALIB_MWA_LONGITUDE_RADIANS, MWALIB_MWA_ALTITUDE_METRES, MWALIB_SPEED_OF_LIGHT_IN_VACUUM_M_PER_S. The constants are prefixed with "MWALIB_" to ensure no clashes with mwa_rust_core constants
* Fixed missing nul terminators on returned strings in mwalib FFI functions

* Fixed bug where the `num_metafits_fine_chan_freqs` and `metafits_fine_chan_freqs_hz` were not being populated correctly for a stand-alone `MetafitsContext` usecase.
* Fixed attribute name `metafits_fine_chan_freqs` to `metafits_fine_chan_freqs_hz` in FFI `MetafitsMetadata`to be consistent with the rest of the library.
* Removed constants `SPEED_OF_LIGHT_IN_VACUUM_M_PER_S`, `MWA_LATITUDE_RADIANS`, `MWA_LONGITUDE_RADIANS`, `MWA_ALTITUDE_METRES` as these are now provided by the [mwa_rust_core](https://github.com/MWATelescope/mwa_rust_core) repo.
* Simplified the dependency rules for `regex` and `rayon` crates.

* Antenna rf_input_x and rf_input_y are now correctly indexed/sorted for the VCSLegacyRecombined case.

* When using a stand-alone MetafitsContext, the rf_inputs are now correctly sorted for the VCSLegacyRecombined case.