Immutability of bundle connections. Furthermore, a copy method is added.

See #30261.

Depends on #31181
Depends on #31182
Depends on #31215
Depends on #31273

CC: @egourgoulhon @tscrim @mkoeppe

Component: manifolds

Keywords: immutability

Author: Michael Jung

Branch/Commit: 70a1d9a

Reviewer: Eric Gourgoulhon

Issue created by migration from https://trac.sagemath.org/ticket/30284