fix(core-api): return the database timestamp instead of deserialised

[faustbrian]

Proposed changes

The timestamp of the deserialised transaction was used instead of the timestamp from the database by which transactions are sorted.

The problem with that is that the timestamp gets overwritten when a transaction gets forged so the timestamp in the database and serialised transaction differ.

Resolves #1951

Types of changes

• Bugfix (non-breaking change which fixes an issue)

Checklist

• I have read the CONTRIBUTING documentation
• Lint and unit tests pass locally with my changes

[codecov-io]

Codecov Report

Merging #1957 into develop will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff            @@
##           develop    #1957   +/-   ##
========================================
  Coverage    38.61%   38.61%           
========================================
  Files          354      354           
  Lines         7762     7762           
  Branches      1137     1139    +2     
========================================
  Hits          2997     2997           
  Misses        4751     4751           
  Partials        14       14

Impacted Files	Coverage Δ
...ore-api/src/versions/1/transactions/transformer.ts	0% <0%> (ø)	⬆️
packages/core-api/src/repositories/transactions.ts	0% <0%> (ø)	⬆️
...ore-api/src/versions/2/transactions/transformer.ts	0% <0%> (ø)	⬆️

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[spkjp]

Looks reasonable.