Replace Maxima with Pynac/Singular in Expression.factor()

[rwst]

The default for symbolic factorization should be changed. Maxima as default should be replaced with a call to Pynac's factor() implementation, which itself uses Singular at the moment. Maxima should be made available via ex.factor(algorithm=...).

As an example of performance gain here one of the Fateman benchmarks:

sage: var('a b c k s y z')
(a, b, c, k, s, y, z)
sage: f = (1+x+y+z)^20+1
sage: g = (f*(f+1)).expand()
sage: %time _=g.factor()

This takes 11 seconds on 8.1.beta5 and 3.3 seconds with Pynac factor (identical time using polynomial ring).

Depends on #23950

CC: @tscrim

Component: symbolics

Author: Ralf Stephan

Branch: 19cff3a

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/23835

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Dependencies: #23861

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Branch: u/rws/replace_maxima_with_pynac_singular_in_expression_factor__

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Changed dependencies from #23861 to pynac-0.7.12

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Commit: 5157371

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Author: Ralf Stephan

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New commits:

5157371

23835: Replace Maxima with Pynac/Singular in Expression.factor()

[rwst]

Description changed:

--- 
+++ 
@@ -1 +1,12 @@
 The default for symbolic factorization should be changed. Maxima as default should be replaced with a call to Pynac's `factor()` implementation, which itself uses Singular at the moment. Maxima should be made available via `ex.factor(algorithm=...)`.
+
+As an example of performance gain here one of the Fateman benchmarks:
+
+```
+sage: var('a b c k s y z')
+(a, b, c, k, s, y, z)
+sage: f = (1+x+y+z)^20+1
+sage: g = (f*(f+1)).expand()
+sage: %time _=g.factor()
+```
+This takes 11 seconds on 8.1.beta5 and 3.3 seconds with Pynac factor (identical time using polynomial ring).

[rwst]

Changed dependencies from pynac-0.7.12 to #23950

[sagetrac-git]

Changed commit from 5157371 to e9484ce