fix: don't add extra newline to command stdout/stderr

[kelly-sovacool]

Changes

shell_run() and exec_in_context() were adding extra newlines to command output, which messed up other functions that used them

Issues

NA

PR Checklist

(~Strikethrough~ any points that are not applicable.)

• [x] This comment contains a description of changes with justifications, with any relevant issues linked.
• [x] Write unit tests for any new features, bug fixes, or other code changes.
• ~[ ] Update docs if there are any API changes.~
• [x] Update CHANGELOG.md with a short description of any user-facing changes and reference the PR number. Guidelines: https://keepachangelog.com/en/1.1.0/

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 35.37%. Comparing base (8de92ce) to head (d8af76e). Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ccbr_tools/shell.py	83.33%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #10 +/- ## ========================================== + Coverage 35.22% 35.37% +0.15% ========================================== Files 13 13 Lines 1042 1046 +4 ========================================== + Hits 367 370 +3 - Misses 675 676 +1 ```

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