recurring issue for small things

[laurgao]

• remove unneeded comment in simplify
• fix this
  
• fix this also (integrand = 2*x+3/(x-3)/(x+3)) (n/a was not an issue, first term of sum is not expanded)
  
• fix this Prod([-Fraction(4, 5), -1**Fraction(5, 2)*x**Fraction(5,2)])
  
• this is because recursive self.is_subtraction = True & keep multiplying by -1 when doing Prod.__repr__. (temporarily patched it so it doesn't fail silently, but idk would need to think of more robust architectural decisions to fix it fr, and i don't rlly see myself encountering this error for now so im just gonna leave it unimplemented.)
  
• (-1)^(5/2) gets displayed as -1^(5/2) which changes meaning in some cases
• sqrt(-x) gets expanded to sqrt(-1)sqrt(x) which is maybe unideal
• cos(x+2pi) & sin(x+2pi) doesn't get converted to cos(x) or sin(x) for some reason (made an xfailed test)
• omg this is rlly bad it doesn't display the brackets? also this should accumulate lmfao
  . there's 2 things here: (1) is prod should show brackets?? or just multiplying a sum by -1 should do it across all terms -> the 2 non-ln terms will accumulate.
• (2) is ln(4) - ln(2) should accumulate. at least for simplify.
• ln(4) + 9/16 - ln(2) gets displayed in this order. pls move all consts to the end.
• fix this
  
• if a term of the solution is constant, rid it?