[TKW] Fixes for @conditional and paged attention

[Hardcode84]

• Fix proxy.create_arg as sympy.StrictlyLessThan and friends are not subclass of sympy.Expr.
• It is now possible to directly use sympy expressions in @conditional arg.
• Fix DCE to not remove ops if they contain nested ops with side-effects (e.g. writes inside conditional).
• Update get_users/get_inputs/node_args ops to properly handle vars captured through placeholders.
• Update CustomOp.erase to cleanup dead captures when deleting placeholders.
• Update paged attention template.