Make changing the QED symbol for some environments easier

[jsimonrichard]

It's possible to change the symbol used at the end of the specific proof environment using the following.

#let proof-nested = thmproof(
  "proof",
  "Proof",
  base: "theorem",
  inset: 0pt,
  bodyfmt: body => [
    #show: thmrules.with(qed-symbol: $square$)
    #proof-bodyfmt(body)
  ]
)

This would work nicely with #25 when used to differentiate which proof is ending.

Would it be possible to make this a simple parameter of the thmproof function in v2.0?