sage.misc.persist: Import SAGE_DB on need only

[mkoeppe]

This eliminates an import-time dependency on sage.misc.misc.

(for #29865)

CC: @fchapoton @kiwifb @embray @tscrim

Component: refactoring

Author: Matthias Koeppe

Branch/Commit: ce63cf5

Reviewer: François Bissey

Issue created by migration from https://trac.sagemath.org/ticket/31332

[mkoeppe]

Branch: u/mkoeppe/sage_misc_persist__import_sage_db_on_need_only

[mkoeppe]

Author: Matthias Koeppe

[mkoeppe]

Commit: ce63cf5

[mkoeppe]

New commits:

ce63cf5

sage.misc.persist: Make import for SAGE_DB local to functions

[kiwifb]

comment:3

This is quite safe after inspection.

[kiwifb]

Reviewer: François Bissey

[mkoeppe]

comment:4

Thanks!

[vbraun]

Changed branch from u/mkoeppe/sage_misc_persist__import_sage_db_on_need_only to ce63cf5