release: bump 0.9.3 -> 0.9.4 (#326)

Packaging fix for the `0.9.3` data layer.

`0.9.3` published to crates.io, Maven Central, NuGet, npm, and the Go mirror, but
the **Linux Python wheels failed to build**, so `Publish to PyPI` was skipped and
no GitHub Release was attached. Root cause: the `live-binance` data layer links
`native-tls` -> `openssl-sys`, and the `manylinux` / `musllinux` wheel-build
containers do not ship the system OpenSSL headers. The native macOS and Windows
wheels were unaffected (system TLS), which is why CI — running Python natively on
the runners, where OpenSSL is present — stayed green.

### Changes
- **`ci`**: install the OpenSSL headers inside the wheel container via
  maturin-action's `before-script-linux` (`openssl-devel` on `manylinux`,
  `openssl-dev` on `musllinux`) before maturin compiles. No library code changed.
- **`release: bump 0.9.3 -> 0.9.4`**: version-string bump across the manual
  touchpoints + `CHANGELOG` `[0.9.4]`.

`0.9.4` is functionally identical to `0.9.3`; it exists only because the already-
published registries cannot re-release `0.9.3`. PyPI publishes for the first time
starting at `0.9.4` (it skips `0.9.3`).

.github/workflows/release.yml

@@ -186,6 +186,14 @@ jobs:
           target: ${{ matrix.target }}
           args: --release --strip --out dist
           manylinux: ${{ matrix.manylinux }}
+          # The live-binance data layer links native-tls -> openssl-sys, which
+          # needs the system OpenSSL headers at build time. The manylinux and
+          # musllinux build containers do not ship them, so install them inside
+          # the container before maturin compiles the wheel (no-op on the native
+          # macOS/Windows runners, where this hook does not run).
+          before-script-linux: |
+            if command -v yum >/dev/null 2>&1; then yum install -y openssl-devel; fi
+            if command -v apk >/dev/null 2>&1; then apk add --no-cache openssl-dev pkgconfig; fi
       - uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           # Include manylinux in the name so the glibc and musl x86_64/aarch64