* change go.mod as first step towards go 1.25
raise minium version of go compatiblity to 1.24.9
and toolchain to be used to 1.25.3
* upgrade .github/workflows and documentation
* update all .github/workflows/ to use the latest version of
actions and the go versions accordingly.
(Only some github actions use a floating tag for the major version.)
* reduce places where the go versions are hardcoded:
* refEr to docs/Development.md from README.md
* use `go.mod` from itest.yml.
* fix itest.yml: checkout before refer to go.mod
* improve code cleanness: use format string w error
and thus makes newer go test versions happy
* update go dependencies
* cleanup some dependencies with go mod tidy
* fix .github/workflows action versions
* fix go action versions
