- Updated pytket version requirement to 1.23.
- `QuantinuumBackend.cost()` now raises an error if the `syntax_checker`
argument doesn't correspond to the device's reported syntax checker or if it
specifies a device that isn't a syntax checker; and the method returns 0 if
called on syntax-checker backends.
- Add partial support for local emulator backends, if installed with the
`pecos` option.