tests(nano): fix flaky test

[glevco]

Motivation

This PR fixes the following 2 flaky tests:

1. test_nc_consensus_success_custom_token
2. test_nc_consensus_success

Acceptance Criteria

• Refactor nanocontracts/test_consensus.py to better handle timestamps.
• Refactor create_tokens on tests/utils.py to prevent it from creating invalid transactions.

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged

[github-actions]

Bencher Report

Branch	tests/nano/fix-flaky
Testbed	ubuntu-22.04

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Benchmark	Latency	Benchmark Result minutes (m) (Result Δ%)	Lower Boundary minutes (m) (Limit %)	Upper Boundary minutes (m) (Limit %)
sync-v2 (up to 20000 blocks)	📈 view plot 🚷 view threshold	1.68 m (+2.47%) Baseline: 1.64 m	1.47 m (87.83%)	1.80 m (93.15%)

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.59%. Comparing base (0faf646) to head (dd9c17e).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1328      +/-   ##
==========================================
- Coverage   85.65%   85.59%   -0.07%     
==========================================
  Files         424      424              
  Lines       31994    31994              
  Branches     4971     4971              
==========================================
- Hits        27406    27386      -20     
- Misses       3595     3605      +10     
- Partials      993     1003      +10     

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