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`).

examples/node/package-lock.json

@@ -14,7 +14,7 @@
     },
     "../../bindings/node": {
       "name": "wickra",
-      "version": "0.9.3",
+      "version": "0.9.4",
       "license": "MIT OR Apache-2.0",
       "devDependencies": {
         "@napi-rs/cli": "^2.18.0"
@@ -23,12 +23,12 @@
         "node": ">= 20"
       },
       "optionalDependencies": {
-        "wickra-darwin-arm64": "0.9.3",
-        "wickra-darwin-x64": "0.9.3",
-        "wickra-linux-arm64-gnu": "0.9.3",
-        "wickra-linux-x64-gnu": "0.9.3",
-        "wickra-win32-arm64-msvc": "0.9.3",
-        "wickra-win32-x64-msvc": "0.9.3"
+        "wickra-darwin-arm64": "0.9.4",
+        "wickra-darwin-x64": "0.9.4",
+        "wickra-linux-arm64-gnu": "0.9.4",
+        "wickra-linux-x64-gnu": "0.9.4",
+        "wickra-win32-arm64-msvc": "0.9.4",
+        "wickra-win32-x64-msvc": "0.9.4"
       }
     },
     "node_modules/wickra": {