Trac #31845: Error when computing norm or trace of inexact zero in Z_q

In !SageMath 9.3:
{{{
sage: R.<a> = Zq(4)
sage: b = a - a
sage: b.trace()
Traceback (most recent call last):
...
AttributeError:
'sage.rings.padics.qadic_flint_CR.qAdicCappedRelativeElement' object has
no attribute 'ground_ring'
}}}
The attached branch fixes this and also changes a few instances of
"norm" to "trace" in the docstring of `trace_unram()`.

URL: https://trac.sagemath.org/31845
Reported by: pbruin
Ticket author(s): Peter Bruin
Reviewer(s): Vincent Delecroix

src/sage/libs/linkages/padics/unram_shared.pxi

@@ -129,6 +129,12 @@ def norm_unram(self, base = None):
         4*7^2 + 7^3 + O(7^22)
         sage: b*b.frobenius()
         4*7^2 + 7^3 + O(7^22)
+
+    Check that :trac:`31845` is fixed::
+
+        sage: R.<a> = Zq(4)
+        sage: (a - a).norm()
+        O(2^20)
     """
     if base is not None:
         if base is self.parent():
@@ -138,7 +144,7 @@ def norm_unram(self, base = None):
     if self._is_exact_zero():
         return self.parent().ground_ring()(0)
     elif self._is_inexact_zero():
-        return self.ground_ring(0, self.valuation())
+        return self.parent().ground_ring()(0, self.valuation())
     if self.valuation() == 0:
         return self.parent().ground_ring()(self.matrix_mod_pn().det())
     else:
@@ -155,10 +161,10 @@ def trace_unram(self, base = None):
     Return the absolute or relative trace of this element.
 
     If ``base`` is given then ``base`` must be a subfield of the
-    parent `L` of ``self``, in which case the norm is the relative
-    norm from `L` to ``base``.
+    parent `L` of ``self``, in which case the trace is the relative
+    trace from `L` to ``base``.
 
-    In all other cases, the norm is the absolute norm down to
+    In all other cases, the trace is the absolute trace down to
     `\QQ_p` or `\ZZ_p`.
 
     EXAMPLES::
@@ -202,6 +208,12 @@ def trace_unram(self, base = None):
         4*5 + 5^2 + 5^3 + 2*5^4
         sage: (a+b).trace()
         4*5 + 5^2 + 5^3 + 2*5^4
+
+    Check that :trac:`31845` is fixed::
+
+        sage: R.<a> = Zq(4)
+        sage: (a - a).trace()
+        O(2^20)
     """
     if base is not None:
         if base is self.parent():
@@ -211,7 +223,7 @@ def trace_unram(self, base = None):
     if self._is_exact_zero():
         return self.parent().ground_ring()(0)
     elif self._is_inexact_zero():
-        return self.ground_ring(0, self.precision_absolute())
+        return self.parent().ground_ring()(0, self.precision_absolute())
     if self.valuation() >= 0:
         return self.parent().ground_ring()(self.matrix_mod_pn().trace())
     else: