chore(cargo): enforce 14-day min-publish-age for crates.io deps

[storopoli]

Description

Adds a 14-day cooldown for crates.io dependencies through Cargo's new min-publish-age setting (RFC 3923), in a root .cargo/config.toml:

[unstable]
min-publish-age = true

[registry]
global-min-publish-age = "14 days"

Dependabot already waits 14 days before proposing a bump. This makes plain cargo add, cargo update, and hand-edited version requirements follow the same rule, so a freshly published (and possibly compromised) release can't slip in through a developer's PR. Versions already in Cargo.lock are left alone. For an urgent fix there is a one-off escape hatch:

CARGO_RESOLVER_INCOMPATIBLE_PUBLISH_AGE=allow cargo update -p <crate>

This repo pins stable Rust. Stable cargo ignores the setting and prints a one-line warning (ignoring registry.global-min-publish-age without -Zmin-publish-age) until Rust 1.100 ships on 2026-11-12. Nothing is enforced before then. The file is in place so the cooldown turns on by itself when the toolchain catches up.

Tracking: STR-3852.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature/Enhancement (non-breaking change which adds functionality or enhances an existing one)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactor
• New or updated tests
• Dependency Update

Notes to Reviewers

One gap worth knowing about: versions already in Cargo.lock are exempt by design, so a lockfile produced with the override still passes cargo build --locked in CI. If we want CI to catch that, cargo update --dry-run prints a Downgrading line for every locked version that violates the policy and can be turned into a check. That is out of scope for this PR.

The [unstable] table is temporary. Stable cargo ignores it, and nightly cargo needs it until the feature reaches stable in Rust 1.100 (2026-11-12). After that it can be dropped.

Verified locally with cargo update --dry-run --workspace:

Locking 0 packages to latest compatible versions
note: pass `--verbose` to see 53 unchanged dependencies behind latest
warning: not updating lockfile due to dry run
Locking 0 packages to highest compatible versions as of 14 days ago

AI disclosure: the change and this PR body were produced with Claude Code and Codex, then reviewed and tested by me.

Is this PR addressing any specification, design doc or external reference document?

• Yes
• No

If yes, please add relevant links:

• https://rust-lang.github.io/rfcs/3923-cargo-min-publish-age.html
• feat(resolver): Stabilize min-publish-age rust-lang/cargo#17335

Checklist

• I have performed a self-review of my code.
• I have commented my code where necessary.
• I have updated the documentation if needed.
• My changes do not introduce new warnings.
• I have added (where necessary) tests that prove my changes are effective or that my feature works.
• New and existing tests pass with my changes.
• I have disclosed my use of AI in the body of this PR.

Related Issues

STR-3852