[DSLX:TIv2] Builtin parametrics of generic "type" do not unify

[cdleary]

Describe the bug
I tried for a while to fix this but want to document since I think I have to put it down for a bit -- the following crashes in IR conversion:

fn f() { assert_eq(1, u32:32) }

Because at IR conversion time it sees u1, u32 in the type info -- this seems incorrect as TIv2 should be creating a single type variable for both operands that has constraints placed on it, since the signature is (T, T) -> () i.e. the constraints to the LHS and RHS should be unified and the concretization would then be identical

Right now you get an error like:

    libc++abi: terminating due to uncaught exception of type absl::lts_20250512::BadStatusOrAccess: Bad StatusOr access: INVALID_ARGUMENT: Could not build IR: Expected operand 1 of eq.5 to have type bits[1], has type bits[32].
    Stack Trace:
    0x1042af2f4: xls::BuilderBase::CreateBValue()
    0x1042b9548: xls::BuilderBase::AddNode<>()
    0x1042b6920: xls::BuilderBase::AddCompareOp()
    0x1042b16e8: xls::BuilderBase::Eq()
    0x102e8dae4: xls::dslx::FunctionConverter::HandleAssertEqBuiltin()
    0x102e8f78c: xls::dslx::FunctionConverter::HandleInvocation()
    0x102e7499c: xls::dslx::FunctionConverterVisitor::Visit()
    0x102eb4b78: std::__1::__variant_detail::__visitation::__base::__dispatcher<>::__dispatch[abi:ne190102]<>()
    0x102ea9834: xls::dslx::FunctionConverter::HandleStatement()
    0x102e7499c: xls::dslx::FunctionConverterVisitor::Visit()
    0x102ea9468: xls::dslx::FunctionConverter::HandleStatementBlock()
    0x102e7499c: xls::dslx::FunctionConverterVisitor::Visit()
    0x102e9f208: xls::dslx::FunctionConverter::HandleFunction()
    0x102e6da1c: xls::dslx::(anonymous namespace)::ConvertCallGraph()
    0x102e6c580: xls::dslx::ConvertModuleIntoPackage()
    0x102e6eed0: xls::dslx::ConvertModuleToPackage()
    0x102e5c70c: xls::dslx::AbstractTestRunner::ParseAndTest()
    0x102e37490: main
    0x19694ab98: start

cc @richmckeever