gh-37207: allow algorithm=pari in LLL
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We allow to call the pari implementation of LLL reduction. The next
release of pari will contain an implementation of the FLATTER algorithm
for LLL reduction, which has better asymptotic complexity.
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URL: https://github.com/sagemath/sage/pull/37207
Reported by: AurelPage
Reviewer(s): AurelPage, Dima Pasechnik, Frédéric Chapoton, Lorenz Panny, Sébastien Labbé, Vincent Delecroix
