Use ambient metric by default in hodge_dual

[tobiasdiez]

If no metric is specified for DiffForm#hodge_dual then now the ambient metric is used by default.

Moreover, I took the opportunity to let DiffFormParal derive from DiffForm, so that the former doesn't need to reimplement hodge_dual.

CC: @tscrim @nthiery @mjungmath @egourgoulhon @mkoeppe

Component: manifolds

Author: Tobias Diez

Branch/Commit: 4e8265d

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/31322

[tobiasdiez]

Author: Tobias Diez

[slel]

Description changed:

--- 
+++ 
@@ -1,3 +1,3 @@
 If no metric is specified for `DiffForm#hodge_dual` then now the ambient metric is used by default.
 
-Moreover, I took the opportunity to let DiffFormParal derive from DiffForm, so that the former doesn't need to reimplement `hodge_dual`.
+Moreover, I took the opportunity to let `DiffFormParal` derive from `DiffForm`, so that the former doesn't need to reimplement `hodge_dual`.

[tscrim]

comment:4

LGTM.

[tscrim]

Reviewer: Travis Scrimshaw

[egourgoulhon]

comment:5

LGTM as well. Thanks for this improvement!

[tobiasdiez]

comment:6

Thanks!

[vbraun]

Changed branch from public/manifolds/hodge_dual_default to 4e8265d