rust: Introduce an `HgError` enum for common error cases Differential Revision: https://phab.mercurial-scm.org/D9892

rust: remove three enums that were identical to `RevlogError` Differential Revision: https://phab.mercurial-scm.org/D9877

rhg: replace `map_*_error` functions with `From` impls Differential Revision: https://phab.mercurial-scm.org/D9876

rust: replace trivial `impl From …` with `#[derive(derive_more::From)]` Crate docs: https://jeltef.github.io/derive_more/derive_more/from.html Differential Revision: https://phab.mercurial-scm.org/D9875

rust: remove `FooError` structs with only `kind: FooErrorKind` enum field Use the enum directly as `FooError` instead. Differential Revision: https://phab.mercurial-scm.org/D9874

rhg: centralize parsing of `--rev` CLI arguments This new module will be the place to implement more of the revset language when we do so. Differential Revision: https://phab.mercurial-scm.org/D9873

rust: Remove hex parsing from the nodemap Separating concerns simplifies error types. Differential Revision: https://phab.mercurial-scm.org/D9864

rust: Make NodePrefix allocation-free and Copy, remove NodePrefixRef The `*Ref` struct only existed to avoid allocating `Vec`s when cloning `NodePrefix`, but we can avoid having `Vec` in the first place by using an inline array instead. This makes `NodePrefix` 21 bytes (with 1 for the length) which is smaller than before as `Vec` alone is 24 bytes. Differential Revision: https://phab.mercurial-scm.org/D9863

churn: count lines that look like diff headers but are not Previously, churn cannot count added lines that start with "++ " or removed lines that start with "-- ". Differential Revision: https://phab.mercurial-scm.org/D9929

rust: Exclude empty node prefixes We presumably don’t want `--rev ""` to select every single revision, even though the empty string is a prefix of all strings. Differential Revision: https://phab.mercurial-scm.org/D9862