rust-regex: increase the DFA size limit for the `regex` crate
`re2`'s DFA limit is already increased in `rust/hg-core/src/re2/rust_re2.cpp`,
the same has to be done for the `regex` crate.
Big repositories with big `.hgignore`s will sometimes hit this limit and face
extreme performance regressions (I've seen one take *minutes* for `hg status`).
Differential Revision: https://phab.mercurial-scm.org/D8499
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