Avoid implicit conversion

[TobiasDuswald]

Addressing the following issues flagged by Sonar: https://sonarcloud.io/project/issues?resolved=false&rules=cpp%3AS1709&types=CODE_SMELL&id=BioDynaMo_biodynamo

Background:

• MISRA C++:2008, 12-1-3 - All constructors that are callable with a single argument of fundamental type shall be declared explicit.
• C++ Core Guidelines C.46 - By default, declare single-argument constructors explicit
• C++ Core Guidelines C.164 - Avoid implicit conversion operators

Significant changes:

1. AgentUid to uint64_t is now explicit (requires casting)
2. LineGraph constructor now takes a pointer to bdm::experimental::Style and not Root::TStyle (conversion in the constructor)
3. AgentPtr to bool kept for convenience.

(1.) should be discussed.

[sonarcloud]

SonarCloud Quality Gate failed.   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

42.9% Coverage
0.0% Duplication