feat: add multiple channel providers

Each provider is enabled via a feature flag.
The currently implemented providers are:
- std::mpsc
- flume
- crossbeam_channel

Cargo.toml

@@ -15,5 +15,24 @@ exclude = ["flake.nix", "flake.lock", ".envrc", "cliff.toml", "release-plz.toml"
 
 [dependencies]
 thiserror = "2.0"
+flume = { version = "0.11", optional = true }
+crossbeam-channel = { version = "0.5", optional = true }
+
+[features]
+default = ["all"]
+
+sync = []
+async = []
+
+sync-std = ["sync"]
+sync-flume = ["sync", "dep:flume"]
+sync-crossbeam = ["sync", "dep:crossbeam-channel"]
+
+all-sync = ["sync-std", "sync-flume", "sync-crossbeam"]
+
+all = ["all-sync"]
 
 [lib]
+
+[package.metadata.docs.rs]
+all-features = true