#1844: Fix VSCode plugin installation progress freezing

[laert-ll]

This PR fixes #1844

Implemented changes:

• The outputListener was called twice per output message: once after stdout finished, once after stderr, iterating the full queue both times. This caused the VSCode plugin progress bar to increment twice per plugin, hitting 100% halfway through making it look frozen. Fix: wait for both streams to finish, then invoke the listener once.

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• When running mvn clean test locally all tests pass and build is successful
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[coveralls]

Coverage Report for CI Build 25334060192

Coverage increased (+0.01%) to 70.657%

Details

• Coverage increased (+0.01%) from the base build.
• Patch coverage: No coverable lines changed in this PR.
• 14 coverage regressions across 1 file.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

14 previously-covered lines in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
com/devonfw/tools/ide/process/ProcessContextImpl.java	14	81.21%

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Coverage Stats

Relevant Lines:	15357
Covered Lines:	11309
Line Coverage:	73.64%
Relevant Branches:	6856
Covered Branches:	4386
Branch Coverage:	63.97%
Branches in Coverage %:	Yes
Coverage Strength:	3.11 hits per line

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💛 - Coveralls

[areinicke]

This seems to work and I don't see any issue with the changes made. Nice job!