Replace unnecessary list of dicts 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"]},
]

A naive guess would be that it's likely not needed to have a list of dicts, and one single dict like so would suffice:

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

If so, the YAML structure could be modified to be the following (note the missing leading - for each subfield within memory_gpu):

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