Remove non-hard dependencies.

[YooSunYoung]

Currently we have non-hard dependencies as a hard-dependencies in pyproject.toml and conda/meta.yml. We should clean them up... I'll do it as I update the copier template.

packages	role
"ess-streaming-data-types"	Flat-buffer (de)serialising
"numpy", "plopp", "sciline", "scipp>23.08.0", "scippneutron"	Data reduction example
"rich"	logging

TODO

• [x] copier update
• [x] import those modules mentioned above, under the method/functions instead of top of the module.
• [x] Remove dependencies and make tests work