refactor: use more specific types in tedge-flows

[didier-wenzek]

Proposed changes

Extract two commits from #3779

• use Duration for on_interval
• use Utf8Path for all paths

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (general improvements like code refactoring that doesn't explicitly fix a bug or add any new functionality)
• Documentation Update (if none of the other choices apply)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Paste Link to the issue

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA (in all commits with git commit -s. You can activate automatic signing by running just prepare-dev once)
• I ran just format as mentioned in CODING_GUIDELINES
• I used just check as mentioned in CODING_GUIDELINES
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

[codecov]

Codecov Report

❌ Patch coverage is 5.26316% with 54 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/extensions/tedge_flows/src/runtime.rs	0.00%	17 Missing ⚠️
crates/core/tedge/src/cli/flows/cli.rs	0.00%	11 Missing ⚠️
crates/extensions/tedge_flows/src/flow.rs	0.00%	10 Missing ⚠️
crates/extensions/tedge_flows/src/config.rs	0.00%	6 Missing ⚠️
crates/extensions/tedge_flows/src/js_script.rs	37.50%	5 Missing ⚠️
crates/core/tedge/src/cli/flows/list.rs	0.00%	2 Missing ⚠️
crates/extensions/tedge_flows/src/lib.rs	0.00%	2 Missing ⚠️
crates/core/tedge/src/cli/flows/test.rs	0.00%	1 Missing ⚠️

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[github-actions]

Robot Results

✅ Passed	❌ Failed	⏭️ Skipped	Total	Pass %	⏱️ Duration
700	0	3	700	100	2h9m29.423177999s