Setigen

* Continuation of the significant plotting overhaul:
* `ftype` and `ttype` for frequency and time axes labels
* frequency labels: ‘fmid’, ‘fmin’, ‘f’, ‘px’
* time labels: ‘same’, ‘trel’, ‘px’
* `swap_axes` parameter to put frequency on the y-axis
* Add new Frame objects; Spectrum and TimeSeries
* Refactor spectrogram integration functions, and adding `stg.spectrum` and `stg.timeseries`)
* Move to `np.random.default_rng` for more robust random seeding
* Update tests

* Fix rng.normal syntax to standard_normal - cupy doesn't have normal() implemented

* Add seeds and RNG handling to every class and function that do random generation (Frame, Antenna, DataStream, etc)
* Complete testing
* Bug fixes related to testing
* Slight refactoring of rarely used functions

* Update MJD in saved filterbank/HDF5 files
* Add `OrderedCadence` object for organizing frames
* Re-vamp plotting for frames and cadences: removes `bl_plot` and fully fleshes out `plot` (with options to plot in terms of relative frequency, absolute frequency, or pixels)
* Important general refactoring
* Add tests for cadence module
* Complete docstrings and documentation

- Support for cadences of frames with the `Cadence` object
- Access and inject signals into individual frames using array indices or slices
- Broadened start time support for individual `Frame` objects
- Ability to truncate using `f_start` and `f_stop` arguments within `Frame` instantiation from real data

- DIRECTIO padding based on header
- record(...load_template=...) argument
- NPOLS not set to 4 instead of 2
- self.time_per_block based on integer self.samples_per_block (previously was real division)