modules: Ignore non-require blocks in go.mod rewrite

modules: Ignore non-require blocks in go.mod rewrite

The Go 1.24 tool directive uses single-token entries inside a
tool ( ... ) block. The previous splitter treated any tab-indented
line as a require entry, causing an index out of range panic when
running hugo mod tidy on a module with a tool block.

Track the require block state explicitly so other blocks (tool,
replace, exclude, retract) are left untouched.

Fixes #14783