Consider making #[fastly::main] comply with clippy::pedantic

[matanlurey]

Most examples of getting started with Rust and Fastly introduce the following pattern:

#[fastly::main]
fn main(req: Request) -> Result<Response, Error> { /* ... */ }

For folks who enable clippy::pedantic, you'll get at least 3 lint warnings:

• clippy::unnecessary_wraps

  Most code samples never return an Error, making Result<Response, Error> unnecessary.

  The macro could allow a return value of pure Response.

• clippy::needless_pass_by_value

  The request object (req: Request) does not always need ownership.

  The macro could allow a parameter of &Request.

• clippy::inline_always

  This is a false-positive, so probably the right thing to do is just tell users using pedantic to ignore it.

It's possible to work around these issues by following the instructions to bootstrap without the macro, or by using #[allow(clippy::lint_warning)] but figured I'd share the feedback anyway and see if any of these were intentional or easy to improve upon or if it's worth documenting using stricter lints with the Fastly Rust API.

Thanks!