rust-node: binary Node ID and conversion utilities The choice of type makes sure that a `Node` has the exact wanted size. We'll use a different type for prefixes. Added dependency: hexadecimal conversion relies on the `hex` crate. The fact that sooner or later Mercurial is going to need to change its hash sizes has been taken strongly in consideration: - the hash length is a constant, but that is not directly exposed to callers. Changing the value of that constant is the only thing to do to change the hash length (even in unit tests) - the code could be adapted to support several sizes of hashes, if that turned out to be useful. To that effect, only the size of a given `Node` is exposed in the public API. - callers not involved in initial computation, I/O and FFI are able to operate without a priori assumptions on the hash size. The traits `FromHex` and `ToHex` have not been directly implemented, so that the doc-comments explaining these restrictions would stay really visible in `cargo doc` Differential Revision: https://phab.mercurial-scm.org/D7788

rust-nodemap: building blocks for nodetree structures This is similar to `nodetreenode` in `revlog.c`. We give it a higher level feeling for ease of handling in Rust context and provide tools for tests and debugging. The encoding choice is dictated by our ultimate goal in this series, that is to make an append-only persistent version of `nodetree`: the 0th Block must be adressed from other Blocks. Differential Revision: https://phab.mercurial-scm.org/D7787

lfs: move the initialization of the upload request into the try block This (almost) guarantees that the file is closed in the case of an exception. The one hole is if the `seek(SEEK_END)`/`tell()`/`seek(0)` sequence fails. But that's going to go away when subclassing `httpconnection.httpsendfile` to fix the worker problem, so I'm not going to worry too much. (And that class appears to have the same problem.) Differential Revision: https://phab.mercurial-scm.org/D7959