feat(utils): Make SlotCalculator instantiable from a chain name (#67)

Right now we have to do error-prone configs everywhere. With this, we won't.

Closes ENG-1139

Author: Evalir

src/utils/calc.rs

@@ -1,4 +1,6 @@
 use crate::utils::from_env::FromEnv;
+use signet_constants::KnownChains;
+use std::str::FromStr;
 
 /// A slot calculator, which can calculate slot numbers, windows, and offsets
 /// for a given chain.
@@ -273,6 +275,22 @@ impl SlotCalculator {
     }
 }
 
+impl From<KnownChains> for SlotCalculator {
+    fn from(value: KnownChains) -> Self {
+        match value {
+            KnownChains::Pecorino => SlotCalculator::pecorino_host(),
+        }
+    }
+}
+
+impl FromStr for SlotCalculator {
+    type Err = signet_constants::ParseChainError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Ok(SlotCalculator::from(KnownChains::from_str(s)?))
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;