♻️ refactor(processor): use reference for GmailClient in processor builder

- modify the `builder` function to accept a reference to `GmailClient` rather than cloning it
- this avoids unnecessary cloning of the `GmailClient`

src/processor.rs

@@ -57,7 +57,7 @@ impl<'a> ProcessorBuilder<'a> {
 
 impl<'a> Processor<'a> {
     /// Initialise a new processor
-    pub fn builder(client: GmailClient, rule: &'a EolRule) -> ProcessorBuilder<'a> {
+    pub fn builder(client: &GmailClient, rule: &'a EolRule) -> ProcessorBuilder<'a> {
         ProcessorBuilder {
             client: client.clone(),
             rule,