CLN: ASV panel_methods
Flake8'd, `param`'d, and this benchmark was timing out on my machine so I scaled down the size of the Panel but should be representative of larger Panels

```
asv dev -b ^panel_methods
· Discovering benchmarks
· Running 2 total benchmarks (1 commits * 1 environments * 2 benchmarks)
[  0.00%] ·· Building for existing-py_home_matt_anaconda_envs_pandas_dev_bin_python
[  0.00%] ·· Benchmarking existing-py_home_matt_anaconda_envs_pandas_dev_bin_python
[ 50.00%] ··· Running panel_methods.PanelMethods.time_pct_change                                                                          ok
[ 50.00%] ···· 
               ======= =======
                 axis         
               ------- -------
                items   1.54s 
                major   1.39s 
                minor   1.41s 
               ======= =======

[100.00%] ··· Running panel_methods.PanelMethods.time_shift                                                                               ok
[100.00%] ···· 
               ======= =======
                 axis         
               ------- -------
                items   397μs 
                major   385μs 
                minor   390μs 
               ======= =======
``` 