[nexus] use raw query builder for sitrep version insertion CTE

[hawkw]

Depends on #9335.

In this comment on PR #9335, @smklein suggested using the raw_query_builder API for writing CTEs, rather than using Diesel's QueryFragment API. This turns out to be a lot less unpleasant and, despite performing less validation of the generated SQL, actually is a lot less likely to introduce hard-to-debug SQL syntax errors. Since most of the query can be written in a single string literal, you actually see more or less what you're gonna get, which is much less obvious with Diesel's API. The InsertSitrepVersionQuery CTE in the same module still uses the QueryFragment API, rather than the raw_query_builder module, since I didn't want to change the existing code in that branch.

This PR refactors the CTE for inserting a new sitrep version to also use raw_query_builder, which is much nicer and should be easier to modify in the future. There should be no functional changes here, just a change to use a different API to generate the query.

Incidentally, this was one of the first times I had real success getting Claude to do a fairly trivial "transform this code from using one API to using another" task --- it wrote most of the first commit, and I tweaked some of its style decisions I didn't love.

[smklein]

nitpick - and I bet this was copied from blueprint insertion, because I made the same change there - but SELECT foo as foo is a bit silly; we can just SELECT version, sitrep_id here