upgrade to 1.25.8 (latest 1.25)

[benoitschipper]

What Changes

• Update the Dockerfile builder stage from golang:1.24-alpine to golang:1.25-alpine to match the go 1.25.8 directive already in go.mod
• Run go get -u ./... and go mod tidy to upgrade all direct and indirect dependencies to their latest compatible versions
• Update go.sum to reflect the new dependency graph
• Update the toolchain-versions spec to reflect Go 1.25 as the minimum required version