Update gofumpt, add go.mod ignore directive (#35434)

gofumpt now
[supports](https://github.com/mvdan/gofumpt/releases/tag/v0.9.0) the
[ignore](https://tip.golang.org/ref/mod#go-mod-file-ignore) directive
added in go 1.25, make use of it which speeds up `make fmt` by around
30%. Likely this also has similar speed gains in other go-related
commands which use the `./...` pattern.

The change in `build/code-batch-process.go` was introduced by `gofumpt`
because of this change:

> A new rule is introduced to "clothe" naked returns for the sake of
clarity. While there is nothing wrong with naming results in function
signatures, using lone return statements can be confusing to the reader.

Makefile

@@ -27,7 +27,7 @@ XGO_VERSION := go-1.25.x
 
 AIR_PACKAGE ?= github.com/air-verse/air@v1
 EDITORCONFIG_CHECKER_PACKAGE ?= github.com/editorconfig-checker/editorconfig-checker/v3/cmd/editorconfig-checker@v3
-GOFUMPT_PACKAGE ?= mvdan.cc/gofumpt@v0.8.0
+GOFUMPT_PACKAGE ?= mvdan.cc/gofumpt@v0.9.1
 GOLANGCI_LINT_PACKAGE ?= github.com/golangci/golangci-lint/v2/cmd/golangci-lint@v2.4.0
 GXZ_PACKAGE ?= github.com/ulikunitz/xz/cmd/gxz@v0.5.15
 MISSPELL_PACKAGE ?= github.com/golangci/misspell/cmd/misspell@v0.7.0