rust-discovery: core implementation for take_quick_sample() This makes in particular `rand` no longer a testing dependency. We keep a seedable random generator on the `PartialDiscovery` object itself, to avoid lengthy initialization. In take_quick_sample() itself, we had to avoid keeping the reference to `self.undecided` to cope with the mutable reference introduced by the the call to `limit_sample`, but it's still manageable without resorting to inner mutability. Sampling being prone to be improved in the mid-term future, testing is minimal, amounting to checking which code path got executed. Differential Revision: https://phab.mercurial-scm.org/D6423

[package]
name = "hg-core"
version = "0.1.0"
authors = ["Georges Racinet <gracinet@anybox.fr>"]
description = "Mercurial pure Rust core library, with no assumption on Python bindings (FFI)"
edition = "2018"

[lib]
name = "hg"

[dependencies]
byteorder = "1.3.1"
lazy_static = "1.3.0"
memchr = "2.2.0"
rand = "> 0.6.4"
rand_pcg = "> 0.1.0"
regex = "^1.1"