ci(rust): add cargo fmt formatting check to CI pipelines

[WilliamBerryiii]

Summary

The repository has no cargo fmt enforcement in CI and no .rustfmt.toml configuration. PR #231 (issue #169) added clippy lint CI but formatting checks were out of scope. This issue adds cargo fmt --check to both GitHub Actions and Azure DevOps pipelines, mirroring the clippy CI structure established in PR #231.

Background

Current State:

• No .rustfmt.toml or rustfmt.toml anywhere in the repository
• No cargo fmt references in any CI pipeline
• Formatting is entirely developer-discretion with no automated enforcement

Existing CI Structure (established by PR #231):

Pipeline	Clippy Workflow	Called From
GitHub Actions	.github/workflows/rust-clippy.yml (reusable)	pr-validation.yml (break_build: true), main.yml (break_build: false)
Azure DevOps	.azdo/templates/rust-clippy-template.yml	azure-pipelines.yml (Main/Scheduled + PR stages)

Both use the same crate discovery pattern: find src/ -name "Cargo.toml" -not -path "./Cargo.toml", detect WASM cdylib crates for --target wasm32-wasip2, and iterate over all 14 crates.

The cargo fmt check should follow this identical structure — parallel reusable workflows/templates alongside the clippy ones.

Acceptance Criteria

• .rustfmt.toml created at repository root with project formatting conventions
• GitHub Actions reusable workflow .github/workflows/rust-fmt.yml created
  • workflow_call with break_build boolean input (matching clippy pattern)
  • Iterates all 14 crates via find src/ -name "Cargo.toml"
  • Runs cargo fmt --check in each crate directory
  • WASM crates use standard cargo fmt --check (rustfmt is target-independent)
• Azure DevOps template .azdo/templates/rust-fmt-template.yml created
  • Same crate discovery and iteration pattern
  • Runs cargo fmt --check in each crate
• pr-validation.yml calls rust-fmt.yml with break_build: true
• main.yml calls rust-fmt.yml with break_build: false
• azure-pipelines.yml calls rust-fmt-template.yml in both Main/Scheduled and PR stages
• All 14 crates pass cargo fmt --check

Implementation Guidance

.rustfmt.toml (Suggested Starting Point)

edition = "2021"

Keep minimal — Rust's default formatting is well-accepted. Add overrides only if the team has specific conventions. Common options to consider:

• max_width = 100 (default is 100)
• use_small_heuristics = "Default" (default)
• imports_granularity = "Crate" (groups imports by crate — requires nightly or recent stable)

GitHub Workflow: .github/workflows/rust-fmt.yml

Mirror .github/workflows/rust-clippy.yml structure:

name: Rust Format Check
on:
  workflow_call:
    inputs:
      break_build:
        required: true
        type: boolean

Key difference from clippy: cargo fmt --check does NOT need --target wasm32-wasip2 — rustfmt operates on source text regardless of compilation target. This simplifies the WASM handling.

Caller Integration Points

pr-validation.yml — add alongside existing clippy call:

rust-fmt:
  needs: [mega-linter]
  uses: ./.github/workflows/rust-fmt.yml
  with:
    break_build: true

main.yml — add alongside existing clippy call:

rust-fmt:
  needs: [mega-linter-main]
  uses: ./.github/workflows/rust-fmt.yml
  with:
    break_build: false

azure-pipelines.yml — add template calls in both stages alongside clippy template calls.

Formatting Fix Command

Before this CI gate is added, run formatting across all crates:

for cargo_toml in $(find src/ -name "Cargo.toml" -not -path "./Cargo.toml"); do
  (cd "$(dirname "$cargo_toml")" && cargo fmt)
done

Related: #169, PR #231 (established the CI pattern), #232 (fix clippy violations)