Add Generics to go-linq

[lonegunmanb]

Hey guys, I like go-linq very much and I'd like to add generics support for this lib long ago, this weekend I've tried.

The trickiest part is how to create parameterized method since golang cannot do that, for example we cannot declare the following method:

func (QueryG[TOut]) GroupJoin[TOut, TInner, TKey, TResult any](inner QueryG[TInner],
	outerKeySelector func(TOut) TKey,
	innerKeySelector func(TInner) TKey,
	resultSelector func(outer TOut, inners []TInner) TResult) QueryG[TResult]

My way is declare some Expander type to do that. For this GroupJoin example:

func TestGroupJoinG(t *testing.T) {
	outer := []int{0, 1, 2}
	inner := []uint{1, 2, 3, 4, 5, 6, 7, 8, 9}
	want := []KeyValueG[int, []uint]{
		{0, []uint{2, 4, 6, 8}},
		{1, []uint{1, 3, 5, 7, 9}},
		{2, []uint{}},
	}

	actual := FromSliceG(outer).Expend4(To4[int, uint, int, KeyValueG[int, []uint]]()).(*Expended4[int, uint, int, KeyValueG[int, []uint]]).GroupJoin(
		FromSliceG(inner),
		func(i int) int { return i },
		func(ui uint) int { return int(ui) % 2 },
		func(outer int, inners []uint) KeyValueG[int, []uint] {
			return KeyValueG[int, []uint]{outer, inners}
		},
	).ToSlice()
	assert.Equal(t, want, actual)
}

We can declare an Expander object to capture the extended type parameters we need, then cast the type immediately, then we decalre these type extended method on these Expander type. The only potential risk point that have no protection from the compiler is this type casting, but they're so close so I think the risk is limited.

This pr is composed to learn go's generics and thanks to @ahmetb I had a lot of fun.