Allow for downloader to use version requirements.

We will soon add support for the compiler version requirement from the
metadata files to be honored. The compiler version is specified in the
solc modes section of the file and its specified as a `VersionReq` and
not as a version.

Therefore, we need to have the ability to honor this version requirement
and find the best version that satisfies the requirement.

crates/core/src/driver/mod.rs

@@ -101,30 +101,12 @@ where
             anyhow::bail!("unsupported solc version: {:?}", &mode.solc_version);
         };
 
-        // Note: if the metadata is contained within a solidity file then this is the only file that
-        // we wish to compile since this is a self-contained test. Otherwise, if it's a JSON file
-        // then we need to compile all of the contracts that are in the directory since imports are
-        // allowed in there.
-        let Some(ref metadata_file_path) = metadata.file_path else {
-            anyhow::bail!("The metadata file path is not defined");
-        };
-        let mut files_to_compile = if metadata_file_path
-            .extension()
-            .is_some_and(|extension| extension.eq_ignore_ascii_case("sol"))
-        {
-            Box::new(std::iter::once(metadata_file_path.clone())) as Box<dyn Iterator<Item = _>>
-        } else {
-            Box::new(
-                FilesWithExtensionIterator::new(metadata.directory()?)
-                    .with_allowed_extension("sol"),
-            )
-        };
-
         let compiler = Compiler::<T::Compiler>::new()
             .allow_path(metadata.directory()?)
             .solc_optimizer(mode.solc_optimize());
-        let mut compiler =
-            files_to_compile.try_fold(compiler, |compiler, path| compiler.with_source(&path))?;
+        let mut compiler = metadata
+            .files_to_compile()?
+            .try_fold(compiler, |compiler, path| compiler.with_source(&path))?;
         for (library_instance, (library_address, _)) in self.deployed_libraries.iter() {
             let library_ident = &metadata
                 .contracts