api/schedule: yield a more informative exception if no operation is found
test/api: exhibit issue if we prepare twice the same thing
api/prepare: make sure we pass correctly the prepared input to the actual task

While doing so we tidy the `cleanup` fixture and use it everywhere, to
kill inter-tests interferences.
api/prepare: handle the input spec protocol
monitor: style
doc: indicate the namespace name
doc: remove reference to sqlalchemy
doc: fix titles
doc: update the repository urls
doc/task: document the `domain` and `timeout` parameters
doc/schedule: fix forgotten domain parameter
doc/inputs: show the task.input value
doc/inputs: add datetime example
inputs/datetime: be more robust with dates at pack time
inputs: add datetime handling
inputs: more robust surrogate input handling
doc: something for the input handling
inputs: compress input data with zstd
tests/inputs: make sure it works with an empty input and refuses invalid input
inputs: automatic marshalling at `schedule` time of the speced inputs