Use caret (`^`) comparison instead of `==` for `required_version`

So, for context, we had only a text comparison for required_version param. Then, on #6066 I introduced semver library so we didn't had to fix this ourselves nor maintain this complexity on this codebase.

One thing tho, is that the only values available for required_version at the time, were exact versions, which would generate an exact match. Which means we were not semver-compliant.

At the time, as this made sense for me to not break change the implementation, we should use == as the default behavior, instead of ^ when there is no operator on it. Because of that, I even opened dtolnay/semver#311 asking semver maintainer to include the option to use other default operator.

The thing is, a few days ago the issue was closed, with this justification:

This diverges from how version requirements with no comparison operator are treated by Cargo.
source: https://github.com/dtolnay/semver/issues/311#issuecomment-3564029577

After digging a bit on that, according to The Cargo Book:

Caret requirements are the default version requirement strategy. This version strategy allows SemVer compatible updates. They are specified as version requirements with a leading caret (^).
source: https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#caret-requirements

With this information, it makes sense to make this semver-compliant and follow the default Cargo behavior.

TL;DR: We should do the same as cargo does and use ^ as the default comparator instead of == which was used to kept the behavior from before we introduced semver-compliant behavior with semver library.

The issue names no files, tests, or entry points. Start by locating the handling of the required_version parameter and review the semver and Cargo caret-requirement references linked in the issue. Done means an omitted comparator follows Cargo's caret behavior instead of exact == matching, with existing behavior covered by tests.