feat: expand the API of SyncDispatcher

[Reasno]

Add more features to the SyncDispatcher. No plan to change contract.Dispatcher yet.

[codecov]

Codecov Report

Merging #191 (6bc5a3a) into master (ecc44a5) will increase coverage by 0.09%.
The diff coverage is 91.52%.

@@            Coverage Diff             @@
##           master     #191      +/-   ##
==========================================
+ Coverage   81.92%   82.02%   +0.09%     
==========================================
  Files          88       88              
  Lines        3309     3366      +57     
==========================================
+ Hits         2711     2761      +50     
- Misses        447      451       +4     
- Partials      151      154       +3     

Impacted Files	Coverage Δ
events/dispatcher.go	92.06% <90.19%> (-7.94%)	⬇️
events/listener.go	100.00% <100.00%> (ø)
config/watcher/file.go	58.13% <0.00%> (-4.66%)	⬇️

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