fix provider loading take two

we previously hoisted this into rust, but we used the try_load feature
which supposedly retains fallbacks. Something about that doesn't behave
the way we expect though and the machinery in providers is sufficiently
complex that we are just going to load the default provider explicitly.

this matches our behavior pre-rust.

Author: reaperhulk

src/rust/src/lib.rs

@@ -24,6 +24,7 @@ mod x509;
 #[pyo3::prelude::pyclass(frozen, module = "cryptography.hazmat.bindings._rust")]
 struct LoadedProviders {
     legacy: Option<provider::Provider>,
+    _default: provider::Provider,
 }
 
 #[pyo3::prelude::pyfunction]
@@ -52,13 +53,14 @@ fn _initialize_legacy_provider() -> CryptographyResult<LoadedProviders> {
         .map(|v| v.is_empty() || v == "0")
         .unwrap_or(true);
     let legacy = if load_legacy {
-        let legacy_result = provider::Provider::try_load(None, "legacy", true);
+        let legacy_result = provider::Provider::load(None, "legacy");
         _legacy_provider_error(legacy_result.is_ok())?;
         Some(legacy_result?)
     } else {
         None
     };
-    Ok(LoadedProviders { legacy })
+    let _default = provider::Provider::load(None, "default")?;
+    Ok(LoadedProviders { legacy, _default })
 }
 
 fn _legacy_provider_error(success: bool) -> pyo3::PyResult<()> {