[IMPROVEMENT] Add sample inventory generation to support systematic regression testing

[03-SudheshnaReddy]

Please prefix your pull request with one of the following: [FEATURE] [FIX] [IMPROVEMENT].

In raising this pull request, I confirm the following (please check boxes):

• [✅ ] I have read and understood the contributors guide.
• [✅ ] I have checked that another pull request for this purpose does not exist.
• [ ✅] I have considered, and confirmed that this submission will be valuable to others.
• [ ✅] I accept that this submission may not be used, and the pull request closed at the will of the maintainer.
• [✅ ] I give this submission freely, and claim no ownership to its content.

My familiarity with the project is as follows (check one):

• I have never used the project.
• [✅ ] I have used the project briefly.
• I have used the project extensively, but have not contributed previously.
• I am an active contributor to the project.

---

This PR adds the first building block for systematic regression testing
as discussed recently.

What this PR does

• Adds a sample inventory utility that inspects samples using ffprobe
  (and CCExtractor output when available)
• Produces structured metadata per sample (container, streams, duration,
  detected caption types)
• Adds unit tests with mocked subprocess output so CI is stable
• Keeps all logic optional and non-fatal when external tools are missing

Why

This improves visibility into what the current sample set actually covers, which helps reason about regression coverage gaps and select a representative regression suite more systematically.
The intent is to strengthen confidence in the Sample Platform so future refactors (legacy C cleanup, Rust work) can proceed more safely.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[03-SudheshnaReddy]

I’ve opened a small follow-up draft PR #1001 that builds on the sample inventory to provide a read-only coverage report for containers and caption types.
The goal is to make current regression coverage gaps visible before further cleanup/refactors.