Allow dashes and underscores in custom index names

Previously, `uv add --index` command threw an error when the index name
included characters like hyphens or underscores.

Closes astral-sh#8315

crates/uv-distribution-types/src/index.rs

@@ -158,7 +158,7 @@ impl FromStr for Index {
  return Err(IndexSourceError::EmptyName);
  }
 
- if name.chars().all(char::is_alphanumeric) {
+ if name.chars().all(|c| c.is_alphanumeric() || c == '-' || c == '_') {
  let url = IndexUrl::from_str(url)?;
  return Ok(Self {
  name: Some(name.to_string()),