revlog: add glue to use a pure-Rust VFS...
revlog: add glue to use a pure-Rust VFS
This will save us a lot of calling back into Python, which is always
horribly expensive.
We are now faster in all benchmarked cases except for `log --patch`
specifically on mozilla-try. Fixing this will happen in a later patch.
```
### data-env-vars.name = mercurial-devel-2024-03-22-ds2-pnm
# benchmark.name = hg.command.cat
# bin-env-vars.hg.flavor = rust
# bin-env-vars.hg.py-re2-module = default
# benchmark.variants.files = all-root
# benchmark.variants.output = plain
# benchmark.variants.rev = tip
e679697a6ca4: 1.760765 ~~~~~
5559d7e63ec3: 1.555513 (-11.66%, -0.21)
### data-env-vars.name = mozilla-try-2024-03-26-ds2-pnm
# benchmark.name = hg.command.cat
# bin-env-vars.hg.flavor = rust
# bin-env-vars.hg.py-re2-module = default
# benchmark.variants.files = all-root
# benchmark.variants.output = plain
# benchmark.variants.rev = tip
e679697a6ca4: 62.848869 ~~~~~
5559d7e63ec3: 58.113051 (-7.54%, -4.74)
### data-env-vars.name = mozilla-try-2024-03-26-ds2-pnm
# benchmark.name = hg.command.log
# bin-env-vars.hg.flavor = rust
# bin-env-vars.hg.py-re2-module = default
# benchmark.variants.limit-rev = 10
# benchmark.variants.patch = yes
# benchmark.variants.rev = none
e679697a6ca4: 3.173532 ~~~~~
5559d7e63ec3: 3.543591 (+11.66%, +0.37)
### data-env-vars.name = mozilla-try-2024-03-26-ds2-pnm
# benchmark.name = hg.command.log
# bin-env-vars.hg.flavor = rust
# bin-env-vars.hg.py-re2-module = default
# benchmark.variants.limit-rev = 1000
# benchmark.variants.patch = no
# benchmark.variants.rev = none
e679697a6ca4: 1.214698 ~~~~~
5559d7e63ec3: 1.192478 (-1.83%, -0.02)
### data-env-vars.name = mozilla-unified-2024-03-22-ds2-pnm
# benchmark.name = hg.command.cat
# bin-env-vars.hg.flavor = rust
# bin-env-vars.hg.py-re2-module = default
# benchmark.variants.files = all-root
# benchmark.variants.output = plain
# benchmark.variants.rev = tip
e679697a6ca4: 56.205474 ~~~~~
5559d7e63ec3: 51.520074 (-8.34%, -4.69)
### data-env-vars.name = mozilla-unified-2024-03-22-ds2-pnm
# benchmark.name = hg.command.log
# bin-env-vars.hg.flavor = rust
# bin-env-vars.hg.py-re2-module = default
# benchmark.variants.limit-rev = 10
# benchmark.variants.patch = yes
# benchmark.variants.rev = none
e679697a6ca4: 2.105419 ~~~~~
5559d7e63ec3: 2.051849 (-2.54%, -0.05)
### data-env-vars.name = mozilla-unified-2024-03-22-ds2-pnm
# benchmark.name = hg.command.log
# bin-env-vars.hg.flavor = rust
# bin-env-vars.hg.py-re2-module = default
# benchmark.variants.limit-rev = 1000
# benchmark.variants.patch = no
# benchmark.variants.rev = none
e679697a6ca4: 0.309960 ~~~~~
5559d7e63ec3: 0.299035 (-3.52%, -0.01)
### data-env-vars.name = tryton-public-2024-03-22-ds2-pnm
# benchmark.name = hg.command.cat
# bin-env-vars.hg.flavor = rust
# bin-env-vars.hg.py-re2-module = default
# benchmark.variants.files = all-root
# benchmark.variants.output = plain
# benchmark.variants.rev = tip
e679697a6ca4: 1.849832 ~~~~~
5559d7e63ec3: 1.805076 (-2.42%, -0.04)
### data-env-vars.name = tryton-public-2024-03-22-ds2-pnm
# benchmark.name = hg.command.log
# bin-env-vars.hg.flavor = rust
# bin-env-vars.hg.py-re2-module = default
# benchmark.variants.limit-rev = 10
# benchmark.variants.patch = yes
# benchmark.variants.rev = none
e679697a6ca4: 0.289521 ~~~~~
5559d7e63ec3: 0.279889 (-3.33%, -0.01)
### data-env-vars.name = tryton-public-2024-03-22-ds2-pnm
# benchmark.name = hg.command.log
# bin-env-vars.hg.flavor = rust
# bin-env-vars.hg.py-re2-module = default
# benchmark.variants.limit-rev = 1000
# benchmark.variants.patch = no
# benchmark.variants.rev = none
e679697a6ca4: 0.332270 ~~~~~
5559d7e63ec3: 0.323324 (-2.69%, -0.01)
```
