Update Rust crate heapless to 0.8

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
heapless	dependencies	minor	0.7 -> 0.8

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Release Notes

japaric/heapless (heapless)

v0.8.0

Compare Source

Added

• Add Clone and PartialEq implementations to HistoryBuffer.
• Added an object pool API. see the pool::object module level doc for details
• Add HistoryBuffer::as_slices()
• Implemented retain for IndexMap and IndexSet.
• Recover StableDeref trait for pool::object::Object and pool::boxed::Box.
• Add polyfills for ESP32S2
• Added String::from_utf8 and String::from_utf8_unchecked.

Changed

• updated from edition 2018 to edition 2021
• [breaking-change] IndexMap and IndexSet now require that keys implement the core::hash::Hash
  trait instead of the hash32::Hash (v0.2.0) trait
• move pool::singleton::Box to the pool::box module
• renamed pool::singleton::Pool to BoxPool and moved it into the pool::box module
• move pool::singleton::arc::Arc to the pool::arc module
• renamed pool::singleton::arc::Pool to ArcPool and moved it into the pool::arc module
• [breaking-change] changed the target support of memory pool API to only support 32-bit x86 and a
  subset of ARM targets. See the module level documentation of the pool module for details
• relax trait requirements on IndexMap and IndexSet.
• export IndexSet and IndexMap iterator types.
• [breaking-change] export IndexMapKeys, IndexMapValues and
  IndexMapValuesMut iterator types.
• [breaking-change] this crate now uses portable-atomic v1.0 instead of atomic-polyfill for emulating
  CAS instructions on targets where they're not natively available.
• [breaking-change] From<&str> for String was replaced with TryFrom<&str> because the From trait must not fail.
• [breaking-change] Renamed Cargo features
  • defmt-impl is now defmt-03
  • ufmt-impl is now ufmt
  • cas is removed, atomic polyfilling is now opt-in via the portable-atomic feature.
• Vec::as_mut_slice is now a public method.

Fixed

• Fixed a dropping_references warning in LinearMap.
• Fixed IndexMap entry API returning wrong slot after an insert on vacant entry. (#​360)

Removed

• [breaking-change] this crate no longer has a Minimum Supported Rust Version (MSRV) guarantee and
  should be used with the latest stable version of the Rust toolchain.

• [breaking-change] removed the Init and Uninint type states from pool::singleton::Box

• [breaking-change] removed the following pool::singleton::Box methods: freeze, forget and init

• [breaking-change] removed the pool::singleton::arc::ArcInner type

• [breaking-change] removed support for attributes from pool! and arc_pool!

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