build(msrv): move brush-interactive and brush[-shell] MSRV to 1.95, leave others as is

[reubeno]

Leaves the workspace-wide rust-version at 1.88.0, for the benefit of our most commonly emebedded library crates (brush-core, brush-parser, brush-builtins, et al.). brush, brush-shell, brush-interactive, and brush-fuzz now move to 1.95.0 on their own. This allows them to raise their MSRVs independently in order to benefit from newer front-end dependencies like reedline.

To make this all work out without requiring xtask to also move forward, we also decouple it from brush-shell. (It previously had a dependency on the latter for help content generation. We now indirect through a gen` example in brush-shell.)

Assisted-By: Claude Opus 5

[Copilot]

🟡 Changes recommended

The new policy conflicts with the immediate speculative MSRV increase, and the upgrade guide misstates Cargo behavior and dependency direction.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Separates application-tier MSRVs from the embeddable library crates and decouples xtask from brush-shell.

Changes:

• Sets application-tier crates to Rust 1.95.0.
• Dynamically excludes higher-MSRV crates from MSRV CI builds.
• Moves artifact generation into a brush-shell example.

File summaries

File	Description
xtask/src/generate.rs	Delegates generation to the new example.
xtask/src/ci.rs	Adapts build-check construction.
xtask/src/check.rs	Adds MSRV-aware workspace exclusions.
xtask/Cargo.toml	Removes shell and generation dependencies.
fuzz/Cargo.toml	Sets application-tier MSRV.
docs/reference/msrv-policy.md	Documents the tiered policy.
docs/how-to/upgrade-msrv.md	Documents upgrade procedures.
Cargo.lock	Relocates generation dependencies.
brush/Cargo.toml	Sets application-tier MSRV.
brush-shell/examples/gen.rs	Implements artifact generation.
brush-shell/Cargo.toml	Registers generator and dependencies.
brush-interactive/Cargo.toml	Sets application-tier MSRV.
.github/workflows/ci.yaml	Configures MSRV build arguments.
.github/copilot-instructions.md	Updates contributor guidance.

Review details

• Files reviewed: 13/14 changed files
• Comments generated: 2
• Review effort level: Balanced

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[github-actions]

Test Results

    5 files     49 suites   21m 36s ⏱️
2 949 tests 2 949 ✅ 0 💤 0 ❌
9 145 runs  9 145 ✅ 0 💤 0 ❌

Results for commit aa848b0.

♻️ This comment has been updated with latest results.

[github-actions]

Performance Benchmark Report

Code Coverage Report: Only Changed Files listed

Package	Base Coverage	New Coverage	Difference
brush-core/src/results.rs	🟢 80.62%	🟢 83.72%	🟢 3.1%
brush-test-harness/src/comparison.rs	🟢 80.13%	🟢 83.97%	🟢 3.84%
brush-test-harness/src/execution.rs	🟢 80.2%	🟢 83.17%	🟢 2.97%
brush-test-harness/src/reporting.rs	🔴 11.62%	🔴 46.48%	🟢 34.86%
brush-test-harness/src/runner.rs	🟢 83.98%	🟢 84.58%	🟢 0.6%
brush-test-harness/src/util.rs	🔴 47.76%	🟠 71.64%	🟢 23.88%
Overall Coverage	🟢 76.4%	🟢 76.83%	🟢 0.43%

Minimum allowed coverage is 70%, this run produced 76.83%
Maximum allowed coverage difference is -5%, this run produced 0.43%

Test Summary: bash-completion test suite

Outcome	Count	Percentage
✅ Pass	1588	75.30
❗️ Error	17	0.81
❌ Fail	150	7.11
⏩ Skip	339	16.07
❎ Expected Fail	13	0.62
✔️ Unexpected Pass	2	0.09
📊 Total	2109	100.00