eth/tracers: prevent the calltracer from crashing

[holiman]

This PR fixes #16426 and #21879.

Note: it does not fix the root problem, just makes it so that the calltracer specifically does not run into it. It will generate an erroneous trace, but should no longer lead to a full scale node-crash.

[holiman]

repro non-crasher:

func TestRecursion(t *testing.T) {
	vmctx := testCtx()
	tracer, err := New(`{
			step: function() {}, 
			fault: function() {},
			result: function() {
				var o = {}
				var x = o
				for (i = 0; i < 1000; i++){
					o.foo = {}
					o = o.foo
				}
				return JSON.stringify(x)
			}}
	`, vmctx.txCtx)
	if err != nil {
		t.Fatal(err)
	}
	out, err := runTrace(tracer, vmctx)
	fmt.Printf("Err: %v\n", err)
	fmt.Printf(string(out))
}

Change return JSON.stringify(x) to return x to make it crash

[karalabe]

Closing in favor of #22857, that one is a generic fix for all tracers and also returns a real error instead of silently stopping tracing midway through.