✨ Generic map and slice serialisers

[acabarbaye]

Description

• extended mapstructure decode
• add ways to flatten and expand maps

Test Coverage

• This change is covered by existing or additional automated tests.
• Manual testing has been performed (and evidence provided) as automated testing was not feasible.
• Additional tests are not required for this change (e.g. documentation update).

[joshjennings98]

Just 2 comments, otherwise I think it is okay