src/encoder/text: Optimize metric formatting

[mxinden]

This pull request addresses the low-hanging-fruits within src/encoder/text.rs with the following commits:

• src/benches&src/bin: Add basic text encoder benchmark

• src/encoder/text: Use write_all instead of write_fmt

  Instead of going through write! which calls write_fmt use write_all directly skipping the additional formatting overhead.

• src/encoder/text: Use regex crate to determine if escaping is needed

  Within escape_string instead of always allocating a new String and iterating through each character one-by-one, first check whether the input string needs any escaping, if not, return without any allocation. If it does need escaping, start from the first occurence.

Benchmark results on a Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz:

$ cargo benchcmp master optimized
 name                                 master ns/iter  optimized ns/iter  diff ns/iter   diff %  speedup 
 bench_text_encoder_with_escaping     131,884,199     105,675,740         -26,208,459  -19.87%   x 1.25 
 bench_text_encoder_without_escaping  117,592,719     73,070,167          -44,522,552  -37.86%   x 1.61

CPU flamegraph before:

CPU flamegraph after:

Memory allocation flamegraph before:

Memory allocation flamegraph after:

[mxinden]

@lucab @kennytm would you mind giving this another review?

[lucab]

LGTM, but leaving some room for others' feedback.

[breezewish]

It's interesting that write! is not efficient as I thought. @kennytm @nrc PTAL

[kennytm]

@breeswish yes std::fmt is not efficient because of the virtual calls, which is why packages like ufmt exists.

[mxinden]

Any further comments on this patch?

@breeswish in case there are no objections, do you want me to merge my own pull-request, or rather always have someone other than the author click the merge button?

[mxinden]

I am guessing there are no objections to this patch. @lucab @breeswish could one of you approve this pull request?

[lucab]

@mxinden stamped I think you can rebase-squash a couple of commits from this branch though. Feel free to self-merge when done.

[breezewish]

@lucab Feel free to just merge PRs :)