Add project `rustfmt.toml` file

[notmandatory]

Describe the enhancement

Add a project wide rustfmt.toml file with configs:

format_code_in_doc_comments
wrap_comments

Use case

A project level config file will make it easier for devs to create uniform comments with formatted code and text.

Additional context

See: bitcoindevkit/rust-esplora-client#95

https://rust-lang.github.io/rustfmt/?version=v1.6.0&search=
https://github.com/rust-lang/rustfmt?tab=readme-ov-file#configuring-rustfmt