perf: Use Cow to avoid creates String on format.

[quake]

This pull request focuses on improving the performance and memory usage of the formatting functions by changing their return types to Cow<str>. This allows the functions to return either borrowed or owned data, reducing unnecessary allocations when the input is not modified.

Most benchmarks gain 10% ~ 20% improvement on my local PC:

format_json             time:   [171.73 µs 172.00 µs 172.28 µs]
                        change: [-17.792% -17.409% -17.049%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 4 outliers among 100 measurements (4.00%)
  4 (4.00%) high mild

format_javascript       time:   [360.43 µs 360.88 µs 361.32 µs]
                        change: [-15.179% -13.906% -12.966%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 3 outliers among 100 measurements (3.00%)
  3 (3.00%) high severe

format_json_2k          time:   [21.865 ms 21.882 ms 21.900 ms]
                        change: [-15.133% -14.999% -14.869%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 3 outliers among 100 measurements (3.00%)
  2 (2.00%) high mild
  1 (1.00%) high severe

format_jupyter          time:   [275.67 µs 276.03 µs 276.38 µs]
                        change: [-7.5263% -7.2771% -7.0001%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 7 outliers among 100 measurements (7.00%)
  4 (4.00%) high mild
  3 (3.00%) high severe

format_markdown         time:   [2.2873 ms 2.2896 ms 2.2923 ms]
                        change: [-14.583% -14.448% -14.325%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 3 outliers among 100 measurements (3.00%)
  1 (1.00%) high mild
  2 (2.00%) high severe

lint_markdown           time:   [2.3867 ms 2.3939 ms 2.4021 ms]
                        change: [-15.337% -15.092% -14.799%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 10 outliers among 100 measurements (10.00%)
  5 (5.00%) high mild
  5 (5.00%) high severe

lint_json               time:   [180.12 µs 180.38 µs 180.64 µs]
                        change: [-19.382% -18.912% -18.449%] (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

lint_html               time:   [694.02 µs 694.96 µs 695.95 µs]
                        change: [-15.000% -14.666% -14.362%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 5 outliers among 100 measurements (5.00%)
  4 (4.00%) high mild
  1 (1.00%) high severe

lint_javascript         time:   [367.04 µs 367.55 µs 368.05 µs]
                        change: [-27.115% -23.420% -20.369%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 5 outliers among 100 measurements (5.00%)

[huacnlee]

我早就想优化这部分了，里面有太多的 format 不断创建新的 String。

Cow 正好解决这个问题，每次应该只有少量的情况有修改。

[huacnlee]

这行注释弄掉了，看起来像 AI 干的 😄

[huacnlee]

Missed changed check here.

[quake]

This is inside the Cow::Owned block, which means it's changed already.

[huacnlee]

Missed changed check here.

[huacnlee]

棒！👍👍👍