fix: checks if a default toolchains has been set

[albersonmiranda]

Closes #326

I'm opening as draft because I'm not sure if this is exaclty what is expected as solution. If it's OK, I'll add a test.

Steps to reproduce:

1. Unset default toolchain with rustup default none. rustup show now returns

installed toolchains
--------------------

error: no default toolchain configured

2. Run rust_sitrep(), which should return

r$> rust_sitrep()
Rust infrastructure sitrep:
✔ "rustup": 1.27.1 (2024-04-24)
✔ "cargo": 1.84.0
ℹ host: aarch64-apple-darwin
ℹ toolchains: stable-aarch64-apple-darwin, 1.59.0-aarch64-apple-darwin, 1.60.0-aarch64-apple-darwin, 1.61.0-aarch64-apple-darwin, 1.63.0-aarch64-apple-darwin, and 1.70.0-aarch64-apple-darwin
! One of these toolchains should be default: stable-aarch64-apple-darwin, 1.59.0-aarch64-apple-darwin, 1.60.0-aarch64-apple-darwin, 1.61.0-aarch64-apple-darwin, 1.63.0-aarch64-apple-darwin, and 1.70.0-aarch64-apple-darwin
ℹ Run e.g. `rustup default stable-aarch64-apple-darwin`

[albersonmiranda]

@Ilia-Kosenkov Is something like this what you had in mind?

[Ilia-Kosenkov]

Yup

[Ilia-Kosenkov]

Hm, try rebasing onto main. The CI went through there

[albersonmiranda]

Hm, try rebasing onto main. The CI went through there

@Ilia-Kosenkov All clear!

[codecov]

Codecov Report

Attention: Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.

Project coverage is 83.20%. Comparing base (3221edc) to head (95049b8).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
R/utils.R	75.00%	1 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
R/rust_sitrep.R	97.43% <100.00%> (+0.13%)	⬆️
R/utils.R	96.00% <75.00%> (-4.00%)	⬇️

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