Use try_fold in default implementation of collect_seq, collect_map

Currently fails to build:

    error: reference to packed field is unaligned
       --> test_suite/tests/test_gen.rs:858:10
        |
    858 | #[derive(Serialize, Deserialize)]
        |          ^^^^^^^^^
        |
    note: the lint level is defined here
       --> test_suite/tests/test_gen.rs:5:9
        |
    5   | #![deny(warnings)]
        |         ^^^^^^^^
        = note: `#[deny(unaligned_references)]` implied by `#[deny(warnings)]`
        = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
        = note: fields of packed structs are not properly aligned, and creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
        = note: this error originates in the derive macro `Serialize` (in Nightly builds, run with -Z macro-backtrace for more info)

    error: reference to packed field is unaligned
       --> test_suite/tests/test_gen.rs:858:21
        |
    858 | #[derive(Serialize, Deserialize)]
        |                     ^^^^^^^^^^^
        |
        = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
        = note: fields of packed structs are not properly aligned, and creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
        = note: this error originates in the derive macro `Deserialize` (in Nightly builds, run with -Z macro-backtrace for more info)

Fix unaligned reference warnings on packed remote def

Currently fails:

    error[E0509]: cannot move out of type `RemotePackedNonCopyDef`, which implements the `Drop` trait
       --> test_suite/tests/test_gen.rs:876:10
        |
    876 | #[derive(Deserialize)]
        |          ^^^^^^^^^^^
        |          |
        |          cannot move out of here
        |          data moved here
        |          move occurs because `__v1` has type `std::string::String`, which does not implement the `Copy` trait
        |
        = note: this error originates in the derive macro `Deserialize` (in Nightly builds, run with -Z macro-backtrace for more info)

Support packed remote struct without destructuring

Enable unsized Map/SeqAccess types to use the impl for &mut