The pattern 'type Alias *Document' does not strip methods under
encoding/json/v2 (GOEXPERIMENT=jsonv2), causing UnmarshalJSON to call
itself infinitely until the goroutine stack overflows (1GB limit).
Change to 'type Alias Document' with (*Alias)(d) cast — the standard
Go pattern that works correctly with both encoding/json v1 and v2.
Adds a regression test that uses debug.SetMaxStack to shrink the
goroutine stack limit to 8MB, making the overflow happen in milliseconds
rather than minutes if the recursion is reintroduced.
Ref: https://github.com/golang/go/issues/75361
Signed-off-by: Benjamin Grandfond <benjamin.grandfond@docker.com>
