fix(deps): update module github.com/cenkalti/backoff/v4 to v4.2.1

[tigrannajaryan]

Replaces #222
Adds go mod tidy on top of it to make sure it build.

[codecov]

Codecov Report

Attention: 130 lines in your changes are missing coverage. Please review.

Comparison is base (efddaa2) 76.11% compared to head (db580cf) 72.60%.
Report is 35 commits behind head on main.

Files	Patch %	Lines
internal/certs.go	0.00%	118 Missing ⚠️
client/internal/httpsender.go	88.00%	2 Missing and 1 partial ⚠️
client/internal/mockserver.go	85.71%	2 Missing and 1 partial ⚠️
server/httpconnection.go	0.00%	2 Missing ⚠️
client/internal/clientcommon.go	90.90%	1 Missing ⚠️
client/internal/packagessyncer.go	0.00%	1 Missing ⚠️
client/internal/receivedprocessor.go	90.90%	1 Missing ⚠️
server/serverimpl.go	95.65%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #225      +/-   ##
==========================================
- Coverage   76.11%   72.60%   -3.52%     
==========================================
  Files          24       25       +1     
  Lines        1834     2022     +188     
==========================================
+ Hits         1396     1468      +72     
- Misses        326      445     +119     
+ Partials      112      109       -3     

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