deep-tier: Go modernizers (`go fix`) available — advisory, apply per package

Nothing failed. This is the weekly advisory from the deep tier's modernize job (#521): what Go's go fix modernizers would change in this repository, kept visible without letting a tool commit on anyone's behalf.

Produced by workflow run: https://github.com/picatz/flowstate/actions/runs/32557148726

go fix modernizers available under ./...

324 site(s) across 119 file(s) and 25 package(s). A further 14 site(s) sit in generated files and are excluded throughout: a generated file is never hand-edited, so a modernization there can only arrive through its generator.

Per #521 these are applied opportunistically, never as a sweep: convert a
package's sites when that package is already open for another reason, so the
conversion rides in a diff a reviewer is reading closely. None of this fixes a
defect, and a mechanical diff thousands of lines long is the shape in which a
real one hides. To apply what is named above, scope go fix to the one package
you are in — go fix ./pkg/flowstate/v1/engine/ — and read the result. Note
that Go's go fix rewrites Go source; this repository's own flow fix rewrites
Flowfiles, and the two are unrelated.

Reproduce locally:

make modernize                                    # the whole module
make modernize PKGS=./pkg/flowstate/v1/engine/    # one package

Start with a package already being changed for another reason, using make modernize PKGS=./pkg/flowstate/v1/engine/ or the corresponding package path listed in the issue. Review the scoped go fix diff carefully, leave generated files untouched, and consider the work done when the package’s named modernizations are applied without a broad mechanical sweep.