Consistent way of using builders and options

[yukibtc]

Currently, around the code, we use both builders and options. Before reach beta or release stage, we should define a standard/common way of using these

Ideally:

• use builders for constructors;
• use options for methods.

Example:

// Constructing -> use a builder
let client = Client::builder().database(database).signer(signer).verify_subscriptions(true).gossip(true).build();

// Method which can be customized -> use options
let opts = SyncOptions::default().direction(..);
let event = client.sync(filter, opts).await?;

[TheAwiteb]

Nice issue number #1000 🎉