feat(events): change empty decoded from None to empty dict

[glevco]

Motivation

Our wallet-service use case requested that empty decoded outputs in events should be represented as {} instead of None.

Acceptance Criteria

• Change empty decoded outputs from None to {}.

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged

[github-actions]

Bencher Report

Branch	feat/events/empty-decoded
Testbed	ubuntu-22.04

Click to view all benchmark results

Benchmark	Latency	Benchmark Result minutes (m) (Result Δ%)	Lower Boundary minutes (m) (Limit %)	Upper Boundary minutes (m) (Limit %)
sync-v2 (up to 20000 blocks)	📈 view plot 🚷 view threshold	1.63 m (+0.01%) Baseline: 1.63 m	1.47 m (89.99%)	1.80 m (90.92%)

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.09%. Comparing base (f534d0d) to head (05429b8).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1250      +/-   ##
==========================================
- Coverage   84.11%   84.09%   -0.02%     
==========================================
  Files         311      311              
  Lines       23868    23864       -4     
  Branches     3651     3649       -2     
==========================================
- Hits        20076    20068       -8     
- Misses       3074     3075       +1     
- Partials      718      721       +3     

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