Changes

fileserver: migrate pingcap/tidb artifact downloads to OCI registry (#4274)

Removes all `fileserver.pingcap.net` references from `pingcap/tidb`
pipelines and jobs, replacing binary artifact fetching with OCI pulls
via `hub-zot.pingcap.net/mirrors/hub`.

## Core pattern change

**Before:**
```groovy
environment { FILE_SERVER_URL = 'http://fileserver.pingcap.net' }
// ...
component.fetchAndExtractArtifact(FILE_SERVER_URL, 'tikv', REFS.base_ref, ...)
component.fetchAndExtractArtifact(FILE_SERVER_URL, 'pd',   REFS.base_ref, ...)
```

**After:**
```groovy
environment { OCI_ARTIFACT_HOST = 'hub-zot.pingcap.net/mirrors/hub' }
// ...
final OCI_TAG_PD   = component.computeArtifactOciTagFromPR('pd',   REFS.base_ref, ...)
final OCI_TAG_TIKV = component.computeArtifactOciTagFromPR('tikv', REFS.base_ref, ...)
// ...
container("utils") {
    dir("bin") {
        retry(3) {
            sh label: 'download tidb components', script: """
                ${WORKSPACE}/scripts/artifacts/download_pingcap_oci_artifact.sh \
                    --pd=${OCI_TAG_PD} --tikv=${OCI_TAG_TIKV}
            """
        }
    }
}
```

## Changes by category

- **~60 integration/check2 test pipelines** (release-6.x →
release-9.0-beta, latest): replaced `fetchAndExtractArtifact` for
tikv/pd with OCI download; added `OCI_TAG_*` declarations; added `utils`
sidecar container to pod templates where missing
- **~13 build pipelines** (`pull_build`, `ghpr_build`): removed
fileserver artifact upload steps and CI-flag curl uploads — builds no
longer push to fileserver
- **`periodics_integration_test.groovy`**: rewrote to use OCI download,
removed sha1-based fileserver tracking
- **Tiflash integration tests**: added `OCI_TAG_TIFLASH`; replaced
tiflash binary and vector-search test data downloads (now pulled from
`ann-benchmarks.com`)
- **Sqllogic pod templates**: init containers now use `oras pull` from
OCI registry instead of `wget` from fileserver
- **`pull_br_integration_test_next_gen/download_tools.sh`**: localstack
binary now fetched from GitHub Releases; removed deprecated
`tikv-importer` download helper
- **`release-6.x/ghpr_unit_test.groovy`**: codecov binary now downloaded
from `uploader.codecov.io`; fileserver-based `junitUrl` cleared
- **`prow-jobs/pingcap/tidb/latest-periodics.yaml`**: updated stale
commented-out codecov URL

<!-- START COPILOT ORIGINAL PROMPT -->



<details>

<summary>Original prompt</summary>

> 
> ----
> 
> *This section details on the original issue you should resolve*
> 
> <issue_title>fileserver: migrate artifacts for
pingcap/tidb</issue_title>
> <issue_description>Replace fileserver.pingcap.net usage for
pingcap/tidb with OCI artifacts in a standard registry.
> 
> Acceptance criteria:
> - No fileserver.pingcap.net references in jobs/pipelines for
pingcap/tidb
> - Artifacts pulled via OCI registry with documented paths
> </issue_description>
> 
> ## Comments on the Issue (you are @copilot in this section)
> 
> <comments>
> </comments>
> 


</details>



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- Fixes PingCAP-QE/ci#4210

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: wuhuizuo <2574558+wuhuizuo@users.noreply.github.com>
Co-authored-by: wuhuizuo <wuhuizuo@126.com>
 (commit: ea9b68c)