feat: add support for package conflicts in alternatives

- Introduced a new `conflicts` field in the `Alternatives` struct to track conflicting packages.
- Updated database schema to include a `conflicts` table and related queries.
- Enhanced package specification handling to include conflicts in TOML serialization and deserialization.
- Modified the interactive package creation to allow input for conflicting packages.
- Updated source repository index creation to handle conflicts and added relevant statistics.
- Adjusted tests to cover new conflicts functionality in package alternatives.

src/deps.rs

@@ -495,6 +495,7 @@ mod tests {
                 "foo-libs".to_string(),
                 crate::package::Alternatives {
                     provides: vec!["libfoo".into()],
+                    conflicts: Vec::new(),
                     replaces: Vec::new(),
                 },
             )]),