Optimize formatting a bit

[pitdicker]

This takes the commits from #1163 that simplify and optimize our formatting code a bit. #1335 took the initial refactor from that PR, so now we can take the more interesting part.

Two commits make better use of match to only accept a formatting item if we also have the date/time/offset fields it needs, instead of using map inside a match arm.

The last commit introduces a couple of optimized number formatting functions. They are the trick that makes our formatting implementations for RFC 2822 and 3339 faster, so lets use them for regular formatting too 😄.

Benchmarks

     Running benches/chrono.rs (target/release/deps/chrono-413c84d256ba35f5)
bench_format            time:   [533.37 ns 535.14 ns 537.22 ns]
                        change: [-22.588% -21.943% -21.284%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 6 outliers among 100 measurements (6.00%)
  3 (3.00%) high mild
  3 (3.00%) high severe

bench_format_with_items time:   [388.35 ns 389.61 ns 391.09 ns]
                        change: [-29.520% -28.855% -28.271%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 1 outliers among 100 measurements (1.00%)
  1 (1.00%) high mild

[codecov]

Codecov Report

Attention: Patch coverage is 94.32624% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 91.80%. Comparing base (7f57dde) to head (e3feef3).

Files	Patch %	Lines
src/format/formatting.rs	94.32%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1558      +/-   ##
==========================================
+ Coverage   91.78%   91.80%   +0.02%     
==========================================
  Files          37       37              
  Lines       18167    18148      -19     
==========================================
- Hits        16674    16661      -13     
+ Misses       1493     1487       -6     

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[djc]

Faster in less code, great work!

[pitdicker]

Thank you 😄.