Feature: use NoopTransactionContext in tests

[paullatzelsperger]

What this PR changes/adds

This PR uses the NoopTransactionContext instead of the LocalTransactionContext. In doing so it also replaces the LocalDataSourceRegistry with a mock and removes the Apache connection pool instances from tests.

Connections are simply kept open during each test method and closed afterwards.

Why it does that

To avoid inter-module dependencies and simplify test setups.

Further notes

In order to not have to wrap the entire Connection class, I opted for the usage of a Mockito spy, that prevents connections from getting closed.

Linked Issue(s)

Closes #1119

Checklist

• added appropriate tests?
• performed checkstyle check locally?
• added/updated copyright headers?
• documented public classes/methods?
• added/updated relevant documentation?
• added relevant details to the changelog? (skip with label no-changelog)
• formatted title correctly? (take a look at the CONTRIBUTING and styleguide for details)

[codecov-commenter]

Codecov Report

Merging #1271 (233bfe8) into main (14009c9) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1271   +/-   ##
=======================================
  Coverage   67.30%   67.30%           
=======================================
  Files         713      713           
  Lines       15697    15697           
  Branches     1036     1036           
=======================================
  Hits        10565    10565           
  Misses       4650     4650           
  Partials      482      482           

Impacted Files	Coverage Δ
...tor/transaction/local/LocalDataSourceRegistry.java	100.00% <100.00%> (ø)

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