Enforce stricter rustfmt rules to prevent style ambiguity

[pgherveou]

by default rustfmt preserve local style, and Claude loves to add semi or bracket where there were none before,
We should make the formatting more strict as this is a bit annoying to remind it constantly not to make unnecessary diff.

Summary

The PR is just updating https://github.com/paritytech/polkadot-sdk/blob/pg/stricter-rustfmt-rules/.rustfmt.toml
every other changes are just the result of running the linter

• Change match_arm_leading_pipes from "Preserve" to "Never" to enforce a single style
• Change trailing_semicolon from false to true to enforce return 42; false unfortunately preserve the local style
• Add normalize_comments = true to normalize comment spacing (e.g., // comment not //comment)
• Add normalize_doc_attributes = true to enforce /// over #[doc = ""]

These changes ensure only one valid formatting style exists, reducing unnecessary diffs in pull requests caused by different but equally valid formatting styles.

Not changed (for now)

The following options also default to "Preserve" but were intentionally not changed due to (even) larger diff impact:

• group_imports - Would enforce import grouping order (std → external → crate) but causes massive import reordering across the codebase
• hex_literal_case - Would enforce 0xABCD vs 0xabcd consistency
• edition 2024 - not sure what that change but it also probably create a big diff

These could be considered in a future PR if the one-time diff cost is acceptable.

[cla-bot-2021]

User @claude, please sign the CLA here.

[bkchr]

/cmd fmt

[AndreiEres]

group_imports - Would enforce import grouping order (std → external → crate) but causes massive import reordering across the codebase

So we should prefer grouping imports already, right?

[bkchr]

So we should prefer grouping imports already, right?

I always combine all the imports and not group them.

[pgherveou]

the only one I would add maybe is edition -> 2024, since this is a disturbing change we are better off doing it now, wdyt?

[paritytech-workflow-stopper]

All GitHub workflows were cancelled due to failure one of the required jobs.
Failed workflow url: https://github.com/paritytech/polkadot-sdk/actions/runs/21513417618
Failed job name: test-doc