CopyTo works incorrectly in some cases

[cthulhu-rider]

CopyTo is provided by several complex struct types. It allows to deep-copy instance for safety

Current Behavior

Container.CopyTo keeps dst attributes when src has none. If dst already had some attributes, resulting copy is incorrect

this could be missed in 2 reasons:

• CopyTo is rarely used
• dst is usually zero: np in this case

Expected Behavior

correct deep copy

Possible Solution

just do it

Steps to Reproduce

func TestCopyReset(t *testing.T) {
	var src, dst Container
	dst.SetAttribute("key", "val")
	src.CopyTo(&dst)
	require.Zero(t, dst.Attribute("key"))
}

Context

maybe there are other cases, review all of them. To force this, i suggest to pre-add corresponding unit tests

Regression

no (at least for noticed case)

Your Environment

• Version of the product used: 0b9bb74

[cthulhu-rider]

session.Container/Object have similar error in Unmarshal(JSON: context fields aint reset

func TestResetContext(t *testing.T) {
	var c session.Container
	c.ForVerb(1)
	require.True(t, c.AssertVerb(1))
	
	require.NoError(t, c.Unmarshal(nil))
	require.False(t, c.AssertVerb(1))
}

---

in total, i suggest to add unit tests for resetting a previously set value for the following methods:

1. CopyTo
2. ReadFromV2 (future FromProtoMessage)
3. Unmarshal
4. UnmarshalJSON

in particular cases, this can be already covered. Example

once all tests are done, some cases incl. mentioned here will FAIL. And then fix