Support JAM codec for bounded collections

[davxy]

Previously, bounded-collections was tightly coupled to scale-codec, which posed limitations as our usage evolved.

For now, in PolkaJam, we're relying on a temporary fork: bounded-collections-next with these changes applied. However, our long-term goal is to have jam-codec supported upstream.

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This PR introduces the following changes:

• Makes the choice of codec optional (though we might retain scale-codec as the default for backward compatibility).
• Uses feature flags and macros to conditionally enable codec-specific code, as jam-codec and scale-codec share an identical API (different in their implementations of integers compact encoding).

[Copilot]

Pull Request Overview

This PR decouples the bounded collections’ codec implementation from a hard dependency on scale-codec by making the codec used optional with feature flags and adding support for jam-codec. Key changes include re-exporting scale-codec as codec in primitive-types, updating dependencies and Cargo.toml files, and refactoring codec implementations across bounded collections using conditional compilation macros.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
primitive-types/impls/codec/src/lib.rs	Re-exports scale-codec as codec to enable optional codec selection.
primitive-types/impls/codec/Cargo.toml	Updates dependency references from codec to scale-codec.
bounded-collections/src/weak_bounded_vec.rs	Removes unconditional codec impls and adds a macro-based conditional implementation for scale-codec and jam-codec.
bounded-collections/src/bounded_vec.rs	Updates attribute derivations and refactors codec decoding via macros.
bounded-collections/src/bounded_btree_set.rs	Refactors codec implementations using macros for both codec libraries.
bounded-collections/src/bounded_btree_map.rs	Refactors codec implementations and removes deprecated helper structs for decoding.
bounded-collections/Cargo.toml	Updates dependency definitions and versions to support jam-codec.
bounded-collections/CHANGELOG.md	Adds a new changelog entry documenting the JAM codec support.
Cargo.toml	Updates root dependency from codec to scale-codec.

Comments suppressed due to low confidence (1)

bounded-collections/src/bounded_btree_map.rs:429

• [nitpick] Consider renaming the macro to a more specific name (e.g., 'bounded_btree_map_codec_impl') to enhance clarity and prevent potential name conflicts in larger modules.

macro_rules! codec_impl {

[bkchr]

Besides the dependency that should be moved, it looks good.