[Merged by Bors] - ATX V2 syntactical validation (no deps)

[poszu]

Description

Syntactically validate ATX V2 pre-downloading the dependencies.

💡 It only supports non-merged and non-marriage ATXs. It fails when it detects one of these (there are tests for this).

The ATX HandlerV2 is a separate structure so implementing it doesn't interfere with the existing handler implementation for V1.

HandlerV2 is a work-in-progress as it is not yet meant to be embedded into the Handler.

Test Plan

Added unit tests for syntactical validation and decoding an ATX V2`

TODO

• Explain motivation or link existing issue(s)
• Test changes and document test plan
• Update documentation as needed
• Update changelog as needed

[codecov]

Codecov Report

Attention: Patch coverage is 87.80488% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 80.7%. Comparing base (c865710) to head (2ccb522).

Files	Patch %	Lines
activation/handler_v2.go	90.9%	3 Missing and 3 partials ⚠️
activation/handler.go	42.8%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #5936   +/-   ##
=======================================
  Coverage     80.7%   80.7%           
=======================================
  Files          290     292    +2     
  Lines        30525   30607   +82     
=======================================
+ Hits         24652   24724   +72     
- Misses        4240    4245    +5     
- Partials      1633    1638    +5     

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[poszu]

bors merge

[spacemesh-bors]

Pull request successfully merged into develop.

Build succeeded:

• ci-status
• systest-status