refactor: result types

[tgntr]

Detailed description:
Remove most result types from the codebase, as they are currently used to wrap the actual value types, which adds complexity and makes the code less readable. This is not needed in Go since it supports multiple return values. There are a few polkadot defined result types that can be encoded just before returning the final result.
Which issue(s) this PR fixes:
Fixes #298

Special notes for your reviewer:

Checklist

• Documentation added
• Tests updated

[codecov]

Codecov Report

Attention: 20 lines in your changes are missing coverage. Please review.

Comparison is base (7ac3439) 80.55% compared to head (03dd40e) 80.85%.

Files	Patch %	Lines
frame/system/module.go	81.81%	3 Missing and 3 partials ⚠️
frame/balances/call_set_balance.go	78.57%	2 Missing and 1 partial ⚠️
frame/balances/genesis_builder.go	25.00%	2 Missing and 1 partial ⚠️
frame/balances/module.go	93.61%	0 Missing and 3 partials ⚠️
frame/balances/call_force_free.go	81.81%	1 Missing and 1 partial ⚠️
frame/balances/call_transfer.go	93.10%	1 Missing and 1 partial ⚠️
execution/types/checked_extrinsic.go	91.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #322      +/-   ##
===========================================
+ Coverage    80.55%   80.85%   +0.30%     
===========================================
  Files          165      163       -2     
  Lines        10841    10568     -273     
===========================================
- Hits          8733     8545     -188     
+ Misses        1798     1732      -66     
+ Partials       310      291      -19     

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[radkomih]

lgtm, only the tests coverage