Enhance Message::parse() to support nested placeholders

[vjik]

Q	A
Is bugfix?	✔️
New feature?	❌
Breaks BC?	❌

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.33%. Comparing base (01eb55f) to head (c5e220d).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #133   +/-   ##
=========================================
  Coverage     99.33%   99.33%           
  Complexity      161      161           
=========================================
  Files            11       11           
  Lines           449      449           
=========================================
  Hits            446      446           
  Misses            3        3           

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