fix: improve spec parsing error messages

[baszalmstra]

Improves error handling of specs that look like matchspecs. The error handler tries to parse the input string as a matchspec and outputs a nice error message that should how it should be added as a detailed spec.

E.g. the following from #1782:

jaxlib = "*cpu*"

now results in:

expected a version specifier but looks like a matchspec, did you mean { version = "*", build = "cpu*" }?

The following from #1785:

libblas = "*=*openblas"

results in:

expected a version specifier but looks like a matchspec, did you mean { version = "*", build = "*openblas" }?

There are still some weird edge cases when specifying a channel inline, as can be seen in the tests. This will be fixed with conda/rattler#810