In this commit, we update every in-tree go.mod to declare go 1.25 and
have CI build with 1.26.3 (Dockerfile uses the golang:1.26-alpine base).
Docs that mention the minimum required Go version are aligned with the
new floor as well.
Fixes#2527, which flagged the README.md / go.mod version mismatch (the
README claimed 1.22 while the root + v2transport go.mod files already
required 1.23.2).
The github markdown interpreter has been changed such that it no longer
allows spaces in between the brackets and parenthesis of links and now
requires a newline in between anchors and other formatting. This
updates all of the markdown files accordingly.
While here, it also corrects a couple of inconsistencies in some of the
README.md files.
