fix(txpool, cmd, gtk): broadcast transactions with zero fee

[b00f]

Description

This PR ensures that transactions with zero fees can be broadcasted to the network, even if the tx-pool rejects them and the configuration does not accept zero-fee transactions.
This way, users can broadcast their transactions with zero fees, but their nodes will still drop them if they are deemed unacceptable.

This PR also refactored the txpool tests and simplify them.

[codecov]

Codecov Report

Attention: Patch coverage is 82.03125% with 23 lines in your changes missing coverage. Please review.

Project coverage is 76.21%. Comparing base (86a8ba9) to head (bf6d0e1).
Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1589      +/-   ##
==========================================
+ Coverage   75.07%   76.21%   +1.14%     
==========================================
  Files         234      236       +2     
  Lines       12156    18230    +6074     
==========================================
+ Hits         9126    13894    +4768     
- Misses       2582     3880    +1298     
- Partials      448      456       +8     

[Ja7ad]

@b00f I think better check daily_limit <= 0 in BasicCheck

	if conf.Fee.DailyLimit <= 0 {
		return ConfigError{
			Reason: "dailyLimit can't be zero",
		}
	}