fix(conf): reject pointer-to-map environment with a clear error

[jaideeppyne]

Fixes #825

Passing a pointer to a map as the environment panicked at compile time:

panic: reflect: call of reflect.Value.Len on ptr to non-array Value

EnvWithCache selects the map branch using the dereferenced value's kind, but then read the length and keys from the original pointer value. This iterates the dereferenced value in the map branch, so a *map env is treated exactly like the map it points to — same strict mode and element types — matching the existing behaviour for pointer-to-struct environments.

Added a regression test under test/issues/825/ covering compile+run, strict unknown-name rejection, and element-type inference through the pointer. It panics on master and passes with this change. gofmt, go vet, and the full suite are green.

[sanmaxdev]

The implementation and focused regression tests pass. Before this lands, please reconcile the behavior with #825: the issue is labeled wontfix, and the maintainer's direction was to reject *map input with an error. This patch instead supports non-nil pointers while nil pointers still panic as an unknown type. A decision on support versus rejection seems needed, along with a nil-pointer test for the chosen contract.

[jaideeppyne]

Reconciled with #825's direction: this now rejects *map rather than supporting it, so the wontfix stands — the only change is turning the opaque reflect: call of reflect.Value.Len on ptr to non-array Value panic into a clear environment must be a map, not a pointer to a map: *map[...].

On the nil-pointer case you flagged: I detect the pointer-to-map by type now, so a nil *map is rejected with the same clear message instead of falling through to the generic unknown type panic. Added a TestIssue825_NilPointer case alongside the non-nil one, and confirmed pointer-to-struct envs are unaffected.