fix: add write access check for install path in one-line installer

[dlachaume]

Content

This PR includes a fix to the one-line installer script to ensure the provided install path is writable before proceeding. This avoids misleading errors when the path is not writable.
The creation of the install path directory has also been moved after the command-line argument parsing step to avoid attempting to create a directory with an undefined value.

Pre-submit checklist

• Branch
  • Tests are provided (if possible)
  • Crates versions are updated (if relevant)
  • CHANGELOG file is updated (if relevant)
  • Commit sequence broadly makes sense
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• PR
  • All check jobs of the CI have succeeded
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• Documentation
  • Update README file (if relevant)
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  • Add ADR blog post or Dev ADR entry (if relevant)
  • No new TODOs introduced

[github-actions]

Test Results

    4 files  ±0    154 suites  ±0   22m 49s ⏱️ -48s
2 121 tests ±0  2 121 ✅ ±0  0 💤 ±0  0 ❌ ±0 
6 478 runs  ±0  6 478 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 08d4683. ± Comparison against base commit a776b3d.

♻️ This comment has been updated with latest results.