Fix Deserialize derive for BrpResponse

[MarcGuiselin]

Objective

Bevy remote's BrpResponse derives serde::Deserialize, but the static lifetime prevents it from actually being so:

let response: BrpResponse = serde_json::from_str(&response)?;
                            ---------------------^^^^^^^^^-
                            |                    |
                            |                    borrowed value does not live long enough
                            argument requires that `response` is borrowed for `'static`

No migration guide needed, since the interface for BrpResponse::new used by downstream implementers remains unchanged.

Solution

Remove the jsonrpc field by writing a custom impl for Serialize & Deserialize, which is the same solution as done previously in #23175.

Testing

This change has a very low impact. Tests pass.

Alternatives

1. Replace jsonrpc with String
2. Replace jsonrpc with Cow

[SpecificProtagonist]

This works, but I think the better solution is to do the same as #23175 and remove the jsonrpc field by writing a custom Serialize&Deserialize implementation.

[MarcGuiselin]

@SpecificProtagonist Done. Sorry for the hiatus, but now this PR should be unblocked from me.

[MarcGuiselin]

@alice-i-cecile I'd be nice to land this in 0.19, since this pr compliments #23175 and corrects some outdated docs leftover from that one