ci: update MSRV to Rust 1.94.1

[zackees]

Summary

• Update the declared workspace MSRV from Rust 1.75 to 1.94.1.
• Update the MSRV workflow job name/toolchain and docs to match the pinned Rust toolchain.

Investigation

The failing MSRV job was running Rust 1.75.0. It first failed while soldr bootstrapped managed zccache, because the current zccache dependency graph includes crates using edition 2024, which Cargo 1.75 cannot parse. After bypassing that locally, the workspace dependency graph itself also contained crates requiring newer Rust, including running-process-core with rust-version = 1.85 and other transitive dependencies requiring Rust 1.8x. Since this repo already pins rust-toolchain.toml to 1.94.1, this PR makes 1.94.1 the explicit MSRV.

Verification

• RUSTUP_TOOLCHAIN=1.94.1 uv run soldr cargo check --workspace
• git diff --check

Summary by CodeRabbit

• Chores
  • Updated the minimum supported Rust version (MSRV) to 1.94.1 across project configuration and documentation files.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 5238e729-9bbb-4b05-ac30-7f592c46b48d

📥 Commits

Reviewing files that changed from the base of the PR and between b05ae69 and af8d9e1.

📒 Files selected for processing (5)

• .github/workflows/README.md
• .github/workflows/msrv.yml
• CLAUDE.md
• Cargo.toml
• docs/DEVELOPMENT.md

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📝 Walkthrough

Walkthrough

The Minimum Supported Rust Version (MSRV) is updated uniformly across the repository from 1.75 to 1.94.1. Changes encompass workflow configuration files, workspace package metadata, and development documentation.

Changes

Cohort / File(s)	Summary
Workflow Configuration .github/workflows/msrv.yml, .github/workflows/README.md	Updated MSRV reference from 1.75 to 1.94.1 in both the workflow definition and its documentation.
Package Metadata Cargo.toml	Updated workspace-wide rust-version requirement from 1.75 to 1.94.1 in [workspace.package].
Development Documentation CLAUDE.md, docs/DEVELOPMENT.md	Updated documented MSRV from 1.75 to 1.94.1 in development guides and contributor documentation.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~4 minutes

Possibly related PRs

• Integrate soldr into build workflows #153: Modifies .github/workflows/msrv.yml to rewrite steps for installing and using soldr, directly overlapping with the workflow file updated in this PR.

Poem

🐰 Hopping through versions, we leap ever higher,
From 1.75 to 1.94.1's much finer fire!
Workflows aligned and the configs set bright,
Documentation updated—the MSRV's just right!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'ci: update MSRV to Rust 1.94.1' clearly and concisely summarizes the primary change: updating the minimum supported Rust version (MSRV) across CI configuration, workflow files, and documentation from 1.75 to 1.94.1.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/msrv-1.94.1

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