Improve caching for HeckeAlgebra

[saraedum]

Hecke algebras use adhoc caching which causes trouble for #11895. This ticket replaces some of the caching with CachedRepresentation and cached_method.

[pbruin]

Doctest failure:

sage -t --long src/sage/modular/hecke/module.py
**********************************************************************
File "src/sage/modular/hecke/module.py", line 1646, in sage.modular.hecke.module.HeckeModule_free_module.system_of_eigenvalues
Failed example:
    [A.system_of_eigenvalues(3) for A in S.decomposition()]
Expected:
    [[1, 1, 0], [1, -1, -alpha - 1]]
Got:
    [[1, 1, 0], [1, -1, 1/2*alpha + 1/2]]
**********************************************************************
1 item had failures:
   1 of  14 in sage.modular.hecke.module.HeckeModule_free_module.system_of_eigenvalues
    [188 tests, 1 failure, 7.24 s]

(The patchbot's git was able to merge the branch, unlike the Trac git plugin.)

---

Last 10 new commits:

​ce27b84	Removed sage.misc.cachefunc.ClearCacheOnPickle
​e27e316	Propagate key of a @cached_method correctly
​94fcddb	Merge branch 'u/saraedum/ticket/16337' of git://trac.sagemath.org/sage into ticket/15692
​72fce8b	Added a pickle parameter for @cached_method
​0717849	Enable pickling of the cache for groebner_basis()
​561072f	Merge branch 'u/saraedum/ticket/15692' of git://trac.sagemath.org/sage into ticket/16321
​c74f601	Fix incorrect usage of key parameter of @cached_method for ambient spaces of modular forms
​034ea7a	HeckeAlgebra and HeckeAlgebra_anemic inherit from CachedRepresentation
​fe5ad0a	HeckeAlgebra uses @cached_method where possible
​fddc853	Fixed the expected output of an unstable eigenvalue test.

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

​c182f40	Remove ClearCacheOnPickle meta class
​e3a7eb4	Do not pickle cached methods
​07af453	Fix incorrect usage of key parameter of @cached_method for ambient spaces of modular forms
​31f5e5b	HeckeAlgebra and HeckeAlgebra_anemic inherit from CachedRepresentation
​7174a49	HeckeAlgebra uses @cached_method where possible
​07a1e2e	Fixed the expected output of an unstable eigenvalue test.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​ec0e799	fix imports in modular forms
​0a78802	fix cached_method key computation in modform.ambient_R

[saraedum]

New commits:

​ec0e799	fix imports in modular forms
​0a78802	fix cached_method key computation in modform.ambient_R

[roed]

I fixed a few problems, with Julian looking over my shoulder.

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New commits:

​37499a4

Actually removed some caches that were partially removed from ambient modular forms spaces

[pbruin]

Merge conflict with #12603.

[aly.deines]

Fixed merge conflict.

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New commits:

​12e9c43

Merged 16339 to develop.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​c803a5f

Fixed some imports.

[mderickx]

Merge conflict with 8.1.beta3 needs to be resolved.

[saraedum]

Since this had positive review only merge commits were added. I guess I can set this back to positive review once the patchbot is happy.

[mderickx]

I would say yes unless the merge conflicts were nontrivial.

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New commits:

​710ab45

Merge branch 'develop' into t/16339/ticket/16339