nodemap: track the total and unused amount of data in the rawdata file
We need to keep that information around:
* total data will allow transaction to start appending new information without
confusing other reader.
* unused data will allow to detect when we should regenerate new rawdata file.
Differential Revision: https://phab.mercurial-scm.org/D7889
[workspace]
members = ["hg-core", "hg-direct-ffi", "hg-cpython"]
exclude = ["chg", "hgcli"]