feat: broadcast frame to cascading zippers

[venjiang]

broadcast frame to cascading zippers

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This change is 

[fanweixiao]

core/frame/meta_frame.go line 17 at r1 (raw file):

	metadata []byte
	sourceID string
	dispatch Dispatch

Is boolean better than Dispatch?

[fanweixiao]

core/frame/data_frame_test.go line 22 at r1 (raw file):

	result = append(result, tidbuf...)
	result = append(result, byte(TagOfSourceID), 0x0)
	result = append(result, byte(TagOfDispatch), 0x1, 0x1)

TagOfDispatch only present when value is true.

Code quote (from source.go):

f.SetDispatch(frame.DispatchBroadcast)

[fanweixiao]

core/frame/data_frame.go line 79 at r1 (raw file):

// Dispatch get dispatch mode
func (d *DataFrame) Dispatch() Dispatch {

should be IsDispatch() better?

[fanweixiao]

Shall we uniform the word, dispatch or broadcast?

[fanweixiao]

Reviewed 8 of 8 files at r1, all commit messages.
Reviewable status: all files reviewed, 4 unresolved discussions (waiting on @venjiang and @wujunzhuo)

[venjiang]

Shall we uniform the word, dispatch or broadcast?

Yeah, It should be named broadcast if there is only one dispatch mode.
Can we have other dispatch modes?