Add a TimeConfigBuilder to avoid further breaking changes

[adriangb]

I noticed while updating pydantic-core that despite efforts to avoid breaking changes adding a field to TimeConfig is indeed a breaking change. I'm adding this TimeConfigBuilder so that we can add more options down the road without a breaking change.

@samuelcolvin I realize we probably think we won't need to add any more options, if you're 100% sure of this please just close this, but I figured since we had 0 a week ago and now have 2...

[adriangb]

please review

[codecov]

Codecov Report

Merging #46 (17a3987) into main (7058870) will increase coverage by 0.02%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #46      +/-   ##
==========================================
+ Coverage   99.07%   99.10%   +0.02%     
==========================================
  Files           6        6              
  Lines         862      890      +28     
==========================================
+ Hits          854      882      +28     
  Misses          8        8              

Impacted Files	Coverage Δ
src/lib.rs	91.66% <ø> (ø)
src/datetime.rs	100.00% <100.00%> (ø)
src/duration.rs	100.00% <100.00%> (ø)
src/time.rs	97.76% <100.00%> (+0.25%)	⬆️

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[samuelcolvin]

I'm a bit confused by why this is necessary and what it does.

I thought you could just do

TimeConfig { unix_timestamp_offset: Some(123), ..Default::default() };

And extra settings added to TimeConfig wouldn't break your code?

[adriangb]

Yes but then you have to force users to do that, and it’s not immediately obvious, eg in pydantic-core that’s not what we did. The builder pattern is meant precisely to address this situation.

[adriangb]

No real performance impact:

 name                             main ns/iter  variable ns/iter  diff ns/iter   diff %  speedup 
 compare_datetime_error_chrono    40            40                           0    0.00%   x 1.00 
 compare_datetime_error_iso8601   141           144                          3    2.13%   x 0.98 
 compare_datetime_error_speedate  10            10                           0    0.00%   x 1.00 
 compare_datetime_ok_chrono       166           166                          0    0.00%   x 1.00 
 compare_datetime_ok_iso8601      82            82                           0    0.00%   x 1.00 
 compare_datetime_ok_speedate     11            11                           0    0.00%   x 1.00 
 compare_duration_ok_iso8601      46            46                           0    0.00%   x 1.00 
 compare_duration_ok_speedate     31            32                           1    3.23%   x 0.97 
 compare_timestamp_ok_chrono      9             9                            0    0.00%   x 1.00 
 compare_timestamp_ok_speedate    8             7                           -1  -12.50%   x 1.14 
 date                             3             3                            0    0.00%   x 1.00 
 dt_custom_tz                     13            13                           0    0.00%   x 1.00 
 dt_naive                         12            13                           1    8.33%   x 0.92 
 format_date                      38            38                           0    0.00%   x 1.00 
 format_date_time                 180           221                         41   22.78%   x 0.81 
 format_time                      50            49                          -1   -2.00%   x 1.02 
 time                             6             8                            2   33.33%   x 0.75 
 x_combined                       92            96                           4    4.35%   x 0.96