Tidy3d

- Solver speed improvement (gain depending on simulation + hardware details).
- Bringing the speed of the non-angled mode solver back to pre-21.4.2 levels.

- Improvements to subpixel averaging for dispersive materials.
- Enabled web login using environment variables ``TIDY3D_USER`` and ``TIDY3D_PASS``.

- Bugfix when running simulation with zero ``run_time``.
- More internal logging.
- Fixed unstable ``'Li1993_293K'`` variant of ``cSi`` in the material library.

- Bugfix when downloading data on Windows.
- Bugfix in material fitting tool when target tolerance is not reached.

- New Gaussian beam source and `example usage <examples/GratingCoupler.html>`__.
- Modal sources and monitors in bent and in angled waveguides with `tutorial <examples/Modes_bent_angled.html>`__.
- Nyquist-limit sampling in frequency-domain monitors (much faster without loss of accuracy).
- Support for Drude model of material dispersion.
- Small bugfixes to some of the other dispersion models.
- PEC boundaries applied by default at the truncation of any boundary with PML, avoiding potential
issues with using periodic boundaries under the PML instead.
- Source normalization no longer adding a spurious frequency-dependent phase to the fields.
- Fixed bug in unpacking monitor fields with symmetries and ``interpolate=False``.
- Lots of streamlining on the backend side.

- Fixed bug with zero-size monitor plotting.
- Fixed bug with empty simulation run introduced in 21.4.0.