Add noexcept throughout

[adamfowleruk]

Please start with a use case description for a USER of this enhancement

[Who] As an embedded developer
[What] I need to ensure my code does not throw exceptions
[Value] In order to achieve reliability

[Who] As an embedded developer
[What] I need to see evidence in the API of no exceptions being thrown (i.e. noexcept)
[Value] In order to be reassured that the API will work on my devices

Describe the potential solution you'd like

A clear and concise description of what you want to happen within Herald.

• Remove all remaining uses of STL classes and functions that are not noexcept
• Mark all methods, constructors, destructors of our Herald classes as noexcept
• Ensure tests for boundary conditions are present for all classes to validate this
• Rebuild zephyr demo apps without std::exception support, and retest

Describe alternatives you've considered

A clear and concise description of any alternative solutions or features you've considered.

Considered leaving it as status quo, but reliability concerns for the upcoming wearable release means this needs addressing.

Additional context

Add any other context or screenshots about the feature request here.

• C++ core guidelines for noexcept: https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Re-noexcept
• noexcept specifier: https://en.cppreference.com/w/cpp/language/noexcept_spec
• noexcept test operator: https://en.cppreference.com/w/cpp/language/noexcept
• noexcept, memory and newlib compliance information: https://miscsolutions.wordpress.com/2019/12/27/using-exceptions-in-c-embedded-software/

Relative priority

Please give an indication of a relative priority for this enhancement.

High for v2.2 due to stability requirements.