fix: improve Go version handling

[mattjohnsonpint]

Description

Currently, the Modus Runtime uses Go 1.23.4, but other projects are targeting Go 1.23.0. This should only be the case for the shared libraries in /lib, because Go 1.23.1 fixed several security-related issues with CVEs. Instead, we should do the following:

• The Modus Runtime should continue to be built with Go 1.23.4, and updated with new Go releases.
• Shared libraries in /lib should continue to target Go 1.23.0 for compatibility. (The consuming app will set the actual Go version used.)
• Examples and test projects in the Modus repo should be updated to Go 1.23.4.
• The minimum version of Go needed to build modus apps should be set to 1.23.1, both in the Modus SDK and in the CLI's version checks. That will ensure that Modus apps will be built with Go 1.23.1 or higher.
• During modus new, after validating that the minimum Go version is met, the CLI should set the version in the created project's go.mod file to the version actually installed. For example, if I have Go 1.23.2, modus new should make me a project with 1.23.2 - even if the version in the template is lower or if there's a higher version available. This mirrors the behavior of go mod init for regular Go projects.

This PR implements these changes.

Checklist

• Code compiles correctly and linting passes locally
• For all code changes, an entry added to the CHANGELOG.md file describing and linking to this PR