fix: expose VyperSourceLocation fields (#333)

Expose individual fields in `VyperSourceLocation` for usage downstream.

This is already the case [for the corresponding solc
fields](https://github.com/foundry-rs/compilers/blob/326f79435783173bacfaaa9162a6b801fb7a7fe3/crates/artifacts/solc/src/error.rs#L8):
```rust
// crates/artifacts/solc/src/error.rs
#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub struct SourceLocation {
    pub file: String,
    pub start: i32,
    pub end: i32,
}

#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub struct SecondarySourceLocation {
    pub file: Option<String>,
    pub start: Option<i32>,
    pub end: Option<i32>,
    pub message: Option<String>,
}
```

Author: 0xpolarzero

crates/artifacts/vyper/src/error.rs

@@ -5,11 +5,11 @@ use std::path::PathBuf;
 
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
 pub struct VyperSourceLocation {
-    file: PathBuf,
+    pub file: PathBuf,
     #[serde(rename = "lineno")]
-    line: Option<u64>,
+    pub line: Option<u64>,
     #[serde(rename = "col_offset")]
-    offset: Option<u64>,
+    pub offset: Option<u64>,
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]