Fix import generic function specification

[Kolterdyx]

This PR adds support for using generic function instances, fixing #2.

I modified the tailIdent function to not skip over the type params when checking for the last identifier

This allows importing the same generic function multiple times with different type parameters:

main.go

package main

type A struct {
	Value int
}

type B struct {
	Value int
}

func Identity[T any](x T) T {
	return x
}

func main() {}

convgen.go

//go:build convgen

package main

import (
	"github.com/sublee/convgen"
)

var mod = convgen.Module(
	convgen.ImportFunc(Identity[int]),
	convgen.ImportFunc(Identity[string]),
)

var A2B = convgen.Struct[A, B](mod)

Result from above:

//go:build !convgen

// Code generated by github.com/sublee/convgen@dev. DO NOT EDIT.
//
package main

// convgen: explicit converters

func A2B(in A) (out B) {
	// A.Value -> B.Value
	{
		out.Value = Identity[int](in.Value)
	}
	return
}

[Kolterdyx]

force push was squashing my commits together into one single change