rust: update to edition2021

[Desiki-high]

Relevant Issue (if applicable)

N/A

Details

Since we are using cargo 1.68.2 we don't need to require edition 2018 any more.

Types of changes

What types of changes does your PullRequest introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation Update (if none of the other choices apply)

Checklist

Go over all the following points, and put an x in all the boxes that apply.

• I have updated the documentation accordingly.
• I have added tests to cover my changes.

[Desiki-high]

I have used cargo fix --edition to make sure no new issues were created. Ref: https://doc.rust-lang.org/edition-guide/editions/transitioning-an-existing-project-to-a-new-edition.html.

[codecov]

Codecov Report

Merging #1522 (1d1ce03) into master (194641a) will decrease coverage by 0.02%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1522      +/-   ##
==========================================
- Coverage   62.73%   62.72%   -0.02%     
==========================================
  Files         129      129              
  Lines       44158    44153       -5     
  Branches    44158    44153       -5     
==========================================
- Hits        27703    27695       -8     
+ Misses      15088    15087       -1     
- Partials     1367     1371       +4     

see 6 files with indirect coverage changes

[imeoer]

LGTM!