Change tracking of `polkadot/master` to `polkadot/stable2503`

[cmichi]

Currently we depend on polkadot-sdk/master everywhere. We should change it and depend on stable2503 instead. Then we can clearly state "ink! v6 is compatible with 2503".

You have to change the dependencies to point to stable2503 in ink, cargo-contract, ink-node (https://github.com/use-ink/ink-node), and docker-images (https://github.com/use-ink/docker-images).

[AlexD10S]

I’ve started the dependency updates for both:

• ink! chore: update dependencies ink#2478
• cargo-contract at chore: update dependencies cargo-contract#2009

I also noticed that ink-examples needs to be updated to align with the new stable2503 release: https://github.com/use-ink/ink-examples/tree/v6.x

[al3mart]

Currently working on syncing ink-node with polkadot-stable2503.
Pushing changes to: https://github.com/use-ink/ink-node/tree/polkadot-stable2503.
New node released: https://github.com/use-ink/ink-node/releases/tag/v0.43.2
And crates published:

• node: https://crates.io/crates/ink-node
• runtime: https://crates.io/crates/ink-node-runtime
• parachain-runtime: https://crates.io/crates/ink-parachain-runtime

[AlexD10S]

Merged the docker-image changes too in use-ink/docker-images#4