tidy: document u64 limit for numeric sort keys

[kn1g78]

The tidy-alphabetical checker uses natural sorting for numeric sequences, parsing each sequence as u64.

Document this limit so that numeric sequences in marked lists remain within the supported range.

Tests:

• cargo test --offline --manifest-path src/tools/tidy/Cargo.toml
• x test tidy

[rustbot]

r? @clubby789

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[clubby789]

Why the switch to ASCII?

[kn1g78]

Why the switch to ASCII?

is_numeric also recognizes Unicode numeric characters, while u64::parse only accepts ASCII digits. Using is_ascii_digit keeps the numeric-run detection consistent with the supported numeric syntax and avoids treating Unicode numerals as numeric runs. Supporting Unicode numeric sorting would require separate handling.

[Kivooeo]

which panicked when a marked list contained a number larger than u64::MAX

how often in practice this happens?

[kn1g78]

which panicked when a marked list contained a number larger than u64::MAX

how often in practice this happens?

this does not currently happen in practice and is unlikely with the existing use cases. This PR is defensive hardening for an undocumented u64 limit in the generic comparator, rather than a fix for an observed failure.

[Kivooeo]

let's just document u64 limit then

[kn1g78]

let's just document u64 limit then

Done. Thank you!

[clubby789]

Please update the PR description. In future, please don't use AI to generate PR descriptions
@bors r+ rollup

[rust-bors]

📌 Commit d4dff69 has been approved by clubby789

It is now in the queue for this repository.

[workingjubilee]

@bors r-

It should have the PR updated for its description first, before approval, because when a rollup is made, that will take the PR description at that moment, not whatever edits are landed. That PR description then becomes a commit message.

[rust-bors]

This pull request was unapproved.

View changes since this unapproval

[kn1g78]

done.