fix(ui): memoize selectors for namespaces

[markphelps]

fixes: FLI-482

Selector selectNamespaces returned a different result when called with the same parameters. This can lead to unnecessary rerenders.
Selectors that return a new reference (such as an object or an array) should be memoized: https://redux.js.org/usage/deriving-data-selectors#optimizing-selectors-with-memoization 
Object { state: {…}, selected: (2) […], selected2: (2) […] }

https://redux.js.org/usage/deriving-data-selectors#optimizing-selectors-with-memoization

[GeorgeMac]

I know all the words, but dont fully understand the meaning 😂

[codecov]

Codecov Report

Merging #1837 (2679a1c) into main (e2faa04) will increase coverage by 0.10%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1837      +/-   ##
==========================================
+ Coverage   71.53%   71.64%   +0.10%     
==========================================
  Files          58       58              
  Lines        5501     5501              
==========================================
+ Hits         3935     3941       +6     
+ Misses       1339     1335       -4     
+ Partials      227      225       -2     

see 1 file with indirect coverage changes

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