Impl `MaxSize` for `heapless::Vec`

[HaoboGu]

Hello, is it possible to implement MaxSize for heapless::Vec? I found that Se/De traits are already implemented, but MaxSize does not:

My Cargo.toml:

heapless = {version = "0.8.0", features = ["serde"] }
postcard = { version = "1", features = ["experimental-derive", "use-defmt", "heapless"] }

My structs:

#[derive(Serialize, Deserialize, Clone, Debug, Format, MaxSize)]
pub struct A<const N: usize> {
    pub value: Vec<u8, N>
}

Error log:

error[E0277]: the trait bound `Vec<u8, N>: MaxSize` is not satisfied
  --> /Users/haobogu/Projects/keyboard/rmk/rmk/src/event.rs:29:16
   |
29 |     pub value: Vec<u8, N>
   |                ^^^^^^^^^^ the trait `MaxSize` is not implemented for `Vec<u8, N>`
   |
   = help: the following other types implement trait `MaxSize`:
             &T
             &mut T
             ()
             (A, B)
             (A, B, C)
             (A, B, C, D)
             (A, B, C, D, E)
             (A, B, C, D, E, F)
           and 41 others

[max-heller]

postcard does actually implement MaxSize for heapless::Vec

postcard/source/postcard/src/max_size.rs

Lines 239 to 243 in f1c89db

	#[cfg(feature = "heapless")]
	#[cfg_attr(docsrs, doc(cfg(feature = "heapless")))]
	impl<T: MaxSize, const N: usize> MaxSize for heapless::Vec<T, N> {
	const POSTCARD_MAX_SIZE: usize = <[T; N]>::POSTCARD_MAX_SIZE + varint_size(N);
	}

... just for a different version of heapless (0.7).

postcard/source/postcard/Cargo.toml

Lines 27 to 28 in f1c89db

	[dependencies.heapless]
	version = "0.7.0"

Unfortunately, postcard can't upgrade its heapless dependency without a breaking change (see #165). However, MaxSize will likely soon be based on postcard-schema's Schema trait (see #179), and postcard-schema has a way to support multiple versions of heapless based on crate features, so the MaxSize rework will likely fix this before postcard 2.0 releases.

postcard/source/postcard-schema/Cargo.toml

Lines 43 to 53 in f1c89db

	[dependencies.heapless_v0_7]
	package = "heapless"
	version = "0.7"
	default-features = false
	optional = true
	[dependencies.heapless_v0_8]
	package = "heapless"
	version = "0.8"
	default-features = false
	optional = true

Closing as redundant with #165 and #179.