`bbox_inches="tight"` hardcoded

All figures are displayed with matplotlib's auto-selection of the crop:

https://github.com/JuliaPy/PythonPlot.jl/blob/fe588f4e3b084b9d0ada8641939c6331def77036/src/PythonPlot.jl#L86

This is a great default.
But sometimes you want to have more control over the bbox (especially when working with extreme aspect ratios, when `"tight"` produces totally different figsizes than what you requested).

Also, if in your rcparams, `savefig.bbox` is set to `"standard"` (the default) and not `"tight"`, then your saved figures will differ from the displayed figures, which is confusing.

So, it would be nice if this hardcoded setting was somehow configureable in PythonPlot.

Start at src/PythonPlot.jl around line 86, where bbox_inches="tight" is hardcoded, and review how matplotlib rcparams currently affect displayed and saved figures. Determine the configuration surface needed for bbox selection; done means callers can control this setting and displayed figures remain consistent with the configured savefig.bbox behavior.

由索引模型根据 Issue 内容生成。