[rqlrewrite/schema] Avoid parsing computed relations for each query
The RQLRelationRewriter is instanciated for each RQL query, it should
avoid parsing computed relations formula by using a cache, which seems rightly
located on the instance's schema.
This brings a *huge* performance boost to some pages on application with a few
computed relations (x4 observed on a client app).
Kudos to Adrien, David and Sylvain.
Closes #17059828
^build$
^dist$
\.egg-info$
^.tox$
^.cache$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
\.pybuild
debian/python-cubicweb
debian/*.log
debian/*.substvars
debian/cubicweb-doc
debian/cubicweb
debian/files
syntax: regexp
.*/data.*/database/.*
.*/data/ldapdb/.*
.*/data/uicache/
.*/data/libpython/cubicweb_.*/i18n/.*\.po
^doc/html/
^doc/doctrees/
^doc/book/en/devweb/js_api/
^doc/_build
^doc/js_api/
test-results.xml