Manifold: Change some methods to generators

[mkoeppe]

Follow-up from #31718.

Manifold:

• atlas() and top_charts() currently return a list
  • change to generators of charts
• coord_changes() currently returns a copy
  • change to generator of pairs ((from, to), map) ... so that dict(M.coord_changes()) will create the copy

CC: @mjungmath @egourgoulhon @tscrim

Component: manifolds

Issue created by migration from https://trac.sagemath.org/ticket/31720

[mkoeppe]

Description changed:

--- 
+++ 
@@ -1,8 +1,8 @@
 Follow-up from #31718.
 
 `Manifold`:
-- `top_charts()` currently returns a list
-  - change to generator of charts
+- `atlas()` and `top_charts()` currently return a list
+  - change to generators of charts
 - `coord_changes()` currently returns a copy
   - change to generator of pairs `((from, to), map)` ... so that `dict(M.coord_changes())` will create the copy