refactor!: remove index from trace

[drmorr0]

Description and Rationale

• Remove the index from the stored trace file: the trace index is used by the trace store to detect when tracked k8s resources (Deployments, e.g.) change. It does this by computing a hash of the spec for the resource, and then storing a new event in the trace if the hash has changed. The driver doesn't care about this hash, and in fact it can be wildly inaccurate (e.g., if a SKEL transform is done, the hash stored in the index will no longer match reality). Since the driver doesn't care, we just remove it from the trace entirely.
• Store a "tracked objects" field in the trace file: we replace the "index" with a tracked objects field, that includes a (currently empty) ResourceMetadata struct. The driver still needs a way to look up whether a resource is in the trace or not, and the next PR after this is going to add fields to the ResourceMetadata struct so that we can track the pod spec template hash values (see the design doc).

How

• TODO

Test Steps

• TODO

Other Notes

• Note that this is a breaking change, old trace files will no longer work with this version of simkube.

• I certify that this PR does not contain any code that has been generated with GitHub Copilot or any other AI-based code generation tool, in accordance with this project's policies.

[codecov]

Codecov Report

❌ Patch coverage is 96.55172% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 79.16%. Comparing base (4ff5124) to head (1c765f0).

Files with missing lines	Patch %	Lines
sk-skel/src/lib.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #263      +/-   ##
==========================================
- Coverage   79.25%   79.16%   -0.09%     
==========================================
  Files          61       61              
  Lines        4010     3999      -11     
==========================================
- Hits         3178     3166      -12     
- Misses        832      833       +1     

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