- Move the "sync" property for RPCs to RPCConfig.
- Unify GDScript annotations into a single one:
- `@rpc(master)` # default
- `@rpc(puppet)`
- `@rpc(any)` # former `@remote`
- Implement three additional `@rpc` options:
- The second parameter is the "sync" option (which also calls the
function locally when RPCing). One of "sync", "nosync".
- The third parameter is the transfer mode (reliable, unreliable,
ordered).
- The third parameter is the channel (unused for now).
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