refactor: drop Boost.SmartPtr dependency

[Becheler]

C++11 comes with std::shared_ptr, making Boost.SmartPtr redundant.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.80%. Comparing base (ecf816b) to head (05ad895).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop      #41   +/-   ##
========================================
  Coverage    92.80%   92.80%           
========================================
  Files            6        6           
  Lines          139      139           
  Branches        48       48           
========================================
  Hits           129      129           
  Misses           6        6           
  Partials         4        4           

Files with missing lines	Coverage Δ
...nclude/boost/property_map/dynamic_property_map.hpp	89.47% <100.00%> (ø)

---

Continue to review full report in Codecov by Harness.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ecf816b...05ad895. Read the comment docs.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.