Deprecate inplace parameter in TrianglePandas.astpye().

[genedan]

Description

The Pandas analogue DataFrame.astype() does not have an inplace parameter. Since inplace replacement is a discouraged practice, I think we should drop this parameter. A search of the codebase and docs yielded no current use cases of this parameter.

Is your feature request aligned with the scope of the package?

• Yes, absolutely!
• No, but it's still worth discussing.
• N/A (this request is not a codebase enhancement).

Describe the solution you'd like, or your current workaround.

No response

Do you have any additional supporting notes?

No response

Would you be willing to contribute this ticket?

• Yes, absolutely!
• Yes, but I would like some help.
• No.