fix(compactor): Fix delete request when using Thanos objstore client with filesystem backend [release-3.7.x]

[loki-gh-app]

Backport eae43e1 from #22809 ^{job run}

---

Summary

The compactor selected the chunk-key encoder via a concrete type assertion on *local.FSObjectClient. With use_thanos_objstore enabled the object client is a *bucket.ObjectClientAdapter, so FSEncoder was skipped and chunks were looked up with raw, un-encoded keys. This diverged from the keys written by the rest of the storage stack (storage.NewChunkClient applies FSEncoder for the thanos filesystem backend), causing chunk rewrites during retention to fail and line-filter delete requests to remain stuck in the received state.

[github-actions]

⚠️ The workflow jobs listed below don't declare a permissions: block and may break when the organization's default GITHUB_TOKEN permissions are restricted to read-only.

Expand for findings

warning[excessive-permissions]: overly broad permissions
  --> ./.github/workflows/operator-images.yaml:1:1
   |
 1 | / name: operator images
 2 | |
 3 | | on:
 4 | |   push:
...  |
45 | |       image_name: "storage-size-calculator"
46 | |       tag: "latest"
   | |____________________^ default permissions used due to no permissions: block
   |
   = note: audit confidence → Medium
   = help: audit documentation → https://docs.zizmor.sh/audits/#excessive-permissions

warning[excessive-permissions]: overly broad permissions
  --> ./.github/workflows/operator-images.yaml:12:3
   |
12 | /   publish-grafana-operator:
13 | |     uses: ./.github/workflows/operator-reusable-image-build.yml
14 | |     with:
15 | |       dockerfile: "operator/Dockerfile"
...  |
18 | |       image_name: "loki-operator"
19 | |       tag: "latest"
   | |                   ^
   | |                   |
   | |___________________this job
   |                     default permissions used due to no permissions: block
   |
   = note: audit confidence → Medium
   = help: audit documentation → https://docs.zizmor.sh/audits/#excessive-permissions

warning[excessive-permissions]: overly broad permissions
  --> ./.github/workflows/operator-images.yaml:21:3
   |
21 | /   publish-openshift-operator:
22 | |     uses: ./.github/workflows/operator-reusable-image-build.yml
23 | |     with:
24 | |       dockerfile: "operator/Dockerfile"
...  |
27 | |       image_name: "loki-operator"
28 | |       tag: "latest"
   | |                   ^
   | |                   |
   | |___________________this job
   |                     default permissions used due to no permissions: block
   |
   = note: audit confidence → Medium
   = help: audit documentation → https://docs.zizmor.sh/audits/#excessive-permissions

warning[excessive-permissions]: overly broad permissions
  --> ./.github/workflows/operator-images.yaml:30:3
   |
30 | /   publish-openshift-bundle:
31 | |     uses: ./.github/workflows/operator-reusable-image-build.yml
32 | |     with:
33 | |       dockerfile: "operator/bundle/openshift/bundle.Dockerfile"
...  |
36 | |       image_name: "loki-operator-bundle"
37 | |       tag: "latest"
   | |                   ^
   | |                   |
   | |___________________this job
   |                     default permissions used due to no permissions: block
   |
   = note: audit confidence → Medium
   = help: audit documentation → https://docs.zizmor.sh/audits/#excessive-permissions

warning[excessive-permissions]: overly broad permissions
  --> ./.github/workflows/operator-images.yaml:39:3
   |
39 | /   publish-openshift-size-calculator:
40 | |     uses: ./.github/workflows/operator-reusable-image-build.yml
41 | |     with:
42 | |       dockerfile: "operator/calculator.Dockerfile"
...  |
45 | |       image_name: "storage-size-calculator"
46 | |       tag: "latest"
   | |                    ^
   | |                    |
   | |____________________this job
   |                      default permissions used due to no permissions: block
   |
   = note: audit confidence → Medium
   = help: audit documentation → https://docs.zizmor.sh/audits/#excessive-permissions