ops: set rust msrv to 1.86 and add test workflow

Rust 1.86 is the latest available version on CI runner.

Signed-off-by: tjh <did:plc:65gha4t3avpfpzmvpbwovss7>

.tangled/workflows/test.yaml

···
+when:
+  - event:
+      - push
+    branch:
+      - main
+
+engine: nixery
+
+dependencies:
+  nixpkgs:
+    - cargo
+    - clang
+    - openssl
+    - pkg-config
+
+steps:
+  - name: Run unit tests
+    command: |
+      export PKG_CONFIG_PATH="${PKG_CONFIG_PATH:+$PKG_CONFIG_PATH:}$(nix build nixpkgs#openssl.dev --no-link --print-out-paths)/lib/pkgconfig"
+      cargo test --workspace
+

Cargo.toml

···
 license = "MIT or Apache-2.0"
 edition = "2024"
 publish = false
+rust-version = "1.86"
 
 [workspace.dependencies]
 identity = { path = "crates/identity" }

crates/identity/src/resolvers.rs

···
                 continue;
             };
 
-            if let Some(old_did) = resolved_did.replace(did.clone())
-                && old_did != did
-            {
-                tracing::error!(
-                    ?handle,
-                    ?did,
-                    ?old_did,
-                    "multiple conflicting DIDs found for handle"
-                );
-                // @TODO Replace this with an error so we can retry with a
-                // recursive dns resolver.
-                return Ok(None);
+            if let Some(old_did) = resolved_did.replace(did.clone()) {
+                if old_did != did {
+                    tracing::error!(
+                        ?handle,
+                        ?did,
+                        ?old_did,
+                        "multiple conflicting DIDs found for handle"
+                    );
+                    // @TODO Replace this with an error so we can retry with a
+                    // recursive dns resolver.
+                    return Ok(None);
+                }
             }
         }
     }

crates/knot/Cargo.toml

···
 license.workspace = true
 edition.workspace = true
 publish.workspace = true
+rust-version.workspace = true
 
 [dependencies]
 anyhow = "1.0.99"

rust-toolchain.toml

···
+[toolchain]
+channel = "1.86"