Remove unnecessary single-element lists in methods database entries

[yousefmoazzam]

An example of the current structure of a methods database entry is the following:

httomo/httomo/methods_database/packages/external/httomolibgpu/httomolibgpu.yaml

Lines 3 to 11 in 4429711

	median_filter:
	pattern: all
	output_dims_change: False
	implementation: gpu_cupy
	save_result_default: False
	memory_gpu:
	- datasets: [tomo]
	- multipliers: [2.1]
	- methods: [direct]

Focusing on the memory_gpu field:

httomo/httomo/methods_database/packages/external/httomolibgpu/httomolibgpu.yaml

Lines 8 to 11 in 4429711

	memory_gpu:
	- datasets: [tomo]
	- multipliers: [2.1]
	- methods: [direct]

its values will get parsed into the following data structure in python:

[
  {"datasets": ["tomo"]},
  {"multipliers": [2.1]},
  {"methods": ["direct"]},
]

In each dict in the top-level list, there is one key-value pair. The value in each key-value pair is a list with a single element, ie:

["tomo"]
[2.1]
["direct"]

A naive guess would be that the list is probably not needed, and would suffice to be parsed into a python data structure as:

[
  {"datasets": "tomo"},
  {"multipliers": 2.1},
  {"methods": "direct"},
]

If the list indeed isn't needed, then the YAML can be changed to the following to avoid the list with a single value inside (note the omission of the square brackets):

memory_gpu: 
  - datasets: tomo 
  - multipliers: 2.1 
  - methods: direct