fix(core-blockchain): invalid timestamp check

[spkjp]

Proposed changes

Timestamp check from #2042 plus unit test.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (improve a current implementation without adding a new feature or fixing a bug)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Build (changes that affect the build system)
• Docs (documentation only changes)
• Test (adding missing tests or fixing existing tests)
• Other... Please describe:

Checklist

• I have read the CONTRIBUTING documentation
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[ghost]

@faustbrian @alexbarnsley - please review this pull request in the next few days. Be sure to explicitly select labels so I know what's going on.

If no reviewer appears after a week, a reminder will be sent out.

[codecov-io]

Codecov Report

Merging #2046 into develop will increase coverage by 0.01%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop    #2046      +/-   ##
===========================================
+ Coverage    73.31%   73.32%   +0.01%     
===========================================
  Files          373      373              
  Lines         8243     8247       +4     
  Branches      1188     1177      -11     
===========================================
+ Hits          6043     6047       +4     
+ Misses        2168     2166       -2     
- Partials        32       34       +2

Impacted Files	Coverage Δ
...kchain/src/processor/handlers/unchained-handler.ts	95.74% <100%> (+0.39%)	⬆️
packages/core-test-utils/src/helpers/container.ts	0% <0%> (ø)	⬆️
packages/core-test-utils/src/generators/wallets.ts	14.28% <0%> (ø)	⬆️

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