chore: bump MSRV to 1.93 and adopt new stdlib helpers

[sandersaares]

Bumps the workspace MSRV from 1.91 to 1.93 to align with the oldest Rust toolchain supported across Microsoft, and adopts a couple of stdlib helpers that became stable in 1.93.

Commit 1 — chore: bump MSRV to 1.93

• Cargo.toml: rust-version = "1.93"
• constants.env: RUST_MSRV=1.93

The workspace was already MSRV-clean on 1.93 — no code changes or new lint suppressions were needed for the bump itself.

Commit 2 — refactor: adopt MSRV 1.93 stdlib improvements

Net: +15 / −96 across 4 files.

Crate	Change
data_privacy/src/redaction_engine.rs	Replaced two local DebugFormatter / DisplayFormatter ZST wrapper structs with core::fmt::from_fn closures in redacted_debug / redacted_display.
data_privacy_core/src/redacted.rs	Replaced the inline Adapter struct in the RedactedToString blanket impl with core::fmt::from_fn.
data_privacy/src/sensitive.rs	Replaced three inline Adapter structs in tests with core::fmt::from_fn.
seatbelt/src/breaker/health.rs	Replaced the manual while let Some(front) = … front() / pop_front() sliding-window expiry with VecDeque::pop_front_if.

core::fmt::from_fn (stable in 1.93) returns a wrapper that implements both Display and Debug from the same closure, so it cleanly subsumes both adapter patterns.

[Copilot]

Pull request overview

This PR raises the workspace minimum supported Rust version (MSRV) from 1.91 to 1.93 and then simplifies several formatting adapters / window-expiry loops by adopting stdlib helpers available in Rust 1.93 (core::fmt::from_fn, VecDeque::pop_front_if).

Changes:

• Bump workspace MSRV to Rust 1.93 in Cargo.toml and constants.env.
• Replace local Display/Debug adapter structs with core::fmt::from_fn wrappers in data_privacy and data_privacy_core.
• Simplify VecDeque sliding-window expiry logic using VecDeque::pop_front_if in seatbelt.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
Cargo.toml	Updates [workspace.package].rust-version to 1.93 (workspace MSRV bump).
constants.env	Updates RUST_MSRV to 1.93 to match the workspace MSRV promise.
crates/data_privacy/src/redaction_engine.rs	Uses core::fmt::from_fn instead of local ZST formatter wrappers for redacted debug/display output.
crates/data_privacy_core/src/redacted.rs	Uses core::fmt::from_fn in the RedactedToString blanket impl instead of an inline adapter struct.
crates/data_privacy/src/sensitive.rs	Refactors tests to use core::fmt::from_fn instead of inline adapter structs for redacted formatting snapshots.
crates/seatbelt/src/breaker/health.rs	Uses VecDeque::pop_front_if for window expiry instead of manual front() + pop_front() looping.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.0%. Comparing base (458971e) to head (7c632d1).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #474   +/-   ##
=======================================
  Coverage   100.0%   100.0%           
=======================================
  Files         313      313           
  Lines       24121    24112    -9     
=======================================
- Hits        24121    24112    -9     

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[sandersaares]

cargo-check-external-types requires 1.92! Parking this until that gets sorted out - we either need to get that tool update or replace it.