models::Version: Change num field to a plain String

[Turbo87]

This PR prepares for semver v1.x no longer having a diesel feature, which would make it much more complicated for us to directly deserialize the SQL column into a semver::Version field. We can deserialize it to a String instead, and only parse it into a semver::Version on demand.

[jtgeibel]

LGTM! It seems there are 4 existing versions that cannot be parsed in semver v1.x due to a leading zero in the pre-release portion. We'll want to do a bit more testing on those when bumping semver, but this seems like the most reasonable approach.

I've tested a few things locally by adding a few version numbers of -1 to the database, which fails to parse with the current semver. When sorting in descending order, it look like any un-parsable versions will appear at the end (in JSON, the frontend does its own sorting and seems to maybe fallback to version id). Filtering bad semvers in TopVersions::from_date_version_pairs just causes the version to be blank on the search results in the worst case (currently only affecting hxgm30-client with only a single invalid version).

@bors r+

[bors]

📌 Commit 7a5e799 has been approved by jtgeibel

[bors]

⌛ Testing commit 7a5e799 with merge b239314...

[bors]

☀️ Test successful - checks-actions
Approved by: jtgeibel
Pushing b239314 to master...