Improve hint for installing meson-python when missing as build backend (#15826)
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## Summary
If a package uses meson-python as backend, it's declared as:
```
[build-system]
build-backend = 'mesonpy'
requires = ['meson-python']
```
Currently, if meson-python is missing, one gets the following hint:
```
Traceback (most recent call last):
File "<string>", line 8, in <module>
import mesonpy as backend
ModuleNotFoundError: No module named 'mesonpy'
hint: This error likely indicates that `sagemath` depends on `mesonpy`, but doesn't declare it as a build
dependency. If `sagemath` is a first-party package, consider adding `mesonpy` to its `build-system.requires`.
Otherwise, either add it to your `pyproject.toml` under:
[tool.uv.extra-build-dependencies]
sagemath = ["mesonpy"]
or `uv pip install mesonpy` into the environment and re-run with `--no-build-isolation`.
```
which is not quite correct as the build backend/module is called
"mesonpy" but the python package one has to install is "meson-python".
This hint is improved in this PR.
<!-- What's the purpose of the change? What does it do, and why? -->
## Test Plan
I didn't yet had a chance to setup a local dev env for testing this.
<!-- How was it tested? -->
uv
4551effe - Improve hint for installing meson-python when missing as build backend (#15826)
