Fix regex error when actix-web feature not enabled

If the crate is built with only the axum feature, compiling the
webfinger account regex will fail with an error "Unicode-aware case
insensitivity matching is not available..." because of the missing
unicode-case feature. This doesn't happen if actix is installed because
it pulls in the regex crate with all features (via [actix-router][0]).

The failure can be demonstrated by reverting this commit's change to
Cargo.toml and running:

    cargo test --no-default-features --features=axum --doc extract_webfinger_name

Resolve this by adding the unicode-case feature to the regex dependency.

[0]: 0e8ed50e3a/actix-router/Cargo.toml (L25)

Cargo.toml

@@ -38,7 +38,7 @@ bytes = "1.4.0"
 futures-core = { version = "0.3.28", default-features = false }
 pin-project-lite = "0.2.9"
 activitystreams-kinds = "0.3.0"
-regex = { version = "1.8.4", default-features = false, features = ["std"] }
+regex = { version = "1.8.4", default-features = false, features = ["std", "unicode-case"] }
 tokio = { version = "1.21.2", features = [
   "sync",
   "rt",

src/fetch/webfinger.rs

@@ -66,6 +66,25 @@ where
 /// request. For a parameter of the form `acct:gargron@mastodon.social` it returns `gargron`.
 ///
 /// Returns an error if query doesn't match local domain.
+///
+///```
+/// # use activitypub_federation::config::FederationConfig;
+/// # use activitypub_federation::traits::tests::DbConnection;
+/// # use activitypub_federation::fetch::webfinger::extract_webfinger_name;
+/// # tokio::runtime::Runtime::new().unwrap().block_on(async {
+/// # let db_connection = DbConnection;
+/// let config = FederationConfig::builder()
+///     .domain("example.com")
+///     .app_data(db_connection)
+///     .build()
+///     .await
+///     .unwrap();
+/// let data = config.to_request_data();
+/// let res = extract_webfinger_name("acct:test_user@example.com", &data).unwrap();
+/// assert_eq!(res, "test_user");
+/// # Ok::<(), anyhow::Error>(())
+/// }).unwrap();
+///```
 pub fn extract_webfinger_name<T>(query: &str, data: &Data<T>) -> Result<String, Error>
 where
     T: Clone,