Add a common crate (#75)

* Add a barebones common crate

* Refactor some code into the common crate

* Add a `ResolverApi` interface.

This commit adds a `ResolverApi` trait to the `format` crate that can be
implemented by any type that can act as a resolver. A resolver is able
to provide information on the chain state. This chain state could be
fresh or it could be cached (which is something that we will do in a
future PR).

This cleans up our crate graph so that `format` is not depending on the
node interactions crate for the `EthereumNode` trait.

* Cleanup the blocking executor

crates/common/src/iterators/files_with_extension_iterator.rs

@@ -0,0 +1,73 @@
+use std::{borrow::Cow, collections::HashSet, path::PathBuf};
+
+/// An iterator that finds files of a certain extension in the provided directory. You can think of
+/// this a glob pattern similar to: `${path}/**/*.md`
+pub struct FilesWithExtensionIterator {
+    /// The set of allowed extensions that that match the requirement and that should be returned
+    /// when found.
+    allowed_extensions: HashSet<Cow<'static, str>>,
+
+    /// The set of directories to visit next. This iterator does BFS and so these directories will
+    /// only be visited if we can't find any files in our state.
+    directories_to_search: Vec<PathBuf>,
+
+    /// The set of files matching the allowed extensions that were found. If there are entries in
+    /// this vector then they will be returned when the [`Iterator::next`] method is called. If not
+    /// then we visit one of the next directories to visit.
+    files_matching_allowed_extensions: Vec<PathBuf>,
+}
+
+impl FilesWithExtensionIterator {
+    pub fn new(root_directory: PathBuf) -> Self {
+        Self {
+            allowed_extensions: Default::default(),
+            directories_to_search: vec![root_directory],
+            files_matching_allowed_extensions: Default::default(),
+        }
+    }
+
+    pub fn with_allowed_extension(
+        mut self,
+        allowed_extension: impl Into<Cow<'static, str>>,
+    ) -> Self {
+        self.allowed_extensions.insert(allowed_extension.into());
+        self
+    }
+}
+
+impl Iterator for FilesWithExtensionIterator {
+    type Item = PathBuf;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some(file_path) = self.files_matching_allowed_extensions.pop() {
+            return Some(file_path);
+        };
+
+        let directory_to_search = self.directories_to_search.pop()?;
+
+        // Read all of the entries in the directory. If we failed to read this dir's entires then we
+        // elect to just ignore it and look in the next directory, we do that by calling the next
+        // method again on the iterator, which is an intentional decision that we made here instead
+        // of panicking.
+        let Ok(dir_entries) = std::fs::read_dir(directory_to_search) else {
+            return self.next();
+        };
+
+        for entry in dir_entries.flatten() {
+            let entry_path = entry.path();
+            if entry_path.is_dir() {
+                self.directories_to_search.push(entry_path)
+            } else if entry_path.is_file()
+                && entry_path.extension().is_some_and(|ext| {
+                    self.allowed_extensions
+                        .iter()
+                        .any(|allowed| ext.eq_ignore_ascii_case(allowed.as_ref()))
+                })
+            {
+                self.files_matching_allowed_extensions.push(entry_path)
+            }
+        }
+
+        self.next()
+    }
+}

crates/common/src/iterators/mod.rs

@@ -0,0 +1,3 @@
+mod files_with_extension_iterator;
+
+pub use files_with_extension_iterator::*;