deps: gate async-std behind async feature

Author: ValuedMammal

Cargo.toml

@@ -17,13 +17,13 @@ name = "esplora_client"
 path = "src/lib.rs"
 
 [dependencies]
-async-std = "1.13.0"
 serde = { version = "1.0", features = ["derive"] }
 bitcoin = { version = "0.32", features = ["serde", "std"], default-features = false }
 hex = { version = "0.2", package = "hex-conservative" }
 log = "^0.4"
 minreq = { version = "2.11.0", features = ["json-using-serde"], optional = true }
 reqwest = { version = "0.11",  features = ["json"], default-features = false, optional = true }
+async-std = { version = "1.13.0", optional = true }
 
 [dev-dependencies]
 serde_json = "1.0"
@@ -38,7 +38,7 @@ blocking-https = ["blocking", "minreq/https"]
 blocking-https-rustls = ["blocking", "minreq/https-rustls"]
 blocking-https-native = ["blocking", "minreq/https-native"]
 blocking-https-bundled = ["blocking", "minreq/https-bundled"]
-async = ["reqwest", "reqwest/socks"]
+async = ["async-std", "reqwest", "reqwest/socks"]
 async-https = ["async", "reqwest/default-tls"]
 async-https-native = ["async", "reqwest/native-tls"]
 async-https-rustls = ["async", "reqwest/rustls-tls"]