chore(conformance): record cachekit-rs's file-backend 1.2.0 and python-frame copies (LAB-8444)

changelog.d/20261008_lab-8444.md

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+### Conformance — cachekit-rs runs file-backend 1.2.0 and python-frame.json
+
+- [`conformance/sdks.json`](conformance/sdks.json) reads cachekit-rs at `b5fb2a6`, which vendors
+  `file-backend.json` `1.2.0` and, for the first time, `python-frame.json` byte for byte
+  ([cachekit-rs#158](https://github.com/cachekit-io/cachekit-rs/pull/158)). In
+  [`conformance/coverage.md`](conformance/coverage.md), cachekit-rs's `FILE-2`, `IOP-19` and
+  `IOP-20` move to `covered`, and `FILE-1`, `FILE-3`, `FILE-4`, `ENC-5`, `ENC-10` and `WIRE-21` to
+  `partial (gap)`.
+- [Feature matrix](sdk-feature-matrix.md#protocol-compliance) **Test vectors in CI** row and note
+  ¹⁶ record the two copies for cachekit-rs, unreleased. The **Storage container** row and note ¹⁵
+  record cachekit-rs's WIRE-21 violations: it decodes cachekit-ts's bare ByteStorage envelope in
+  every release and on `main`, and crates.io 0.10.0 decodes a CK frame in auto mode. On `main`,
+  on a client without encryption, cachekit-rs refuses every CK frame in `python-frame.json`.
+  WIRE-21's gap in [`conformance/requirements.json`](conformance/requirements.json) names the
+  bare-envelope decode.