Disable default features for `glam`

[Jondolf]

Objective

Currently, the convert-glamXYZ features add glam as a dependency with default features enabled. This unconditionally enables the std feature in glam, making it impossible to use nalgebra and glam interoperatively with the type conversions in no_std environments.

Solution

Disable default features from the glam dependencies. To make CI pass, std is still used if it's enabled for nalgebra.

Note that I also bumped the rustc version to 1.81.0 here since CI was failing because of it (unrelated to this PR).

[Ralith]

Seems like a good idea to me, but this PR seems to contain unrelated changes, e.g. to the rustc version used for trybuild tests.

[Jondolf]

Yeah that's to make CI pass. Won't be needed if we first merge #1505 or some other PR that bumps the version

[sebcrozet]

Thanks!