Improve StringStream handling

[dabonnie]

Description

As done in #28, istringstream handling should throw an exception, rather than relying on nested if statements.

Test Plan

• Manual testing
• Unit test for new classes

Documentation Plan

• update class documentation with throws

Release Plan

• check in PR

Acceptance Criteria

• Code has been implemented, reviewed and merged.
• Test plan has been completed
• Release plan has been completed

Once all above items are checked, this story can be closed.

[zmichaels11]

For context:

 std::stringstream ss
 ss.exceptions(std::ios::failbit | std::ios::badbit);
 // operations on ss go here

[zmichaels11]

It doesn't look like this story is relevant anymore since there is no branching in any code using stringstream.
https://github.com/ros-tooling/system_metrics_collector/search?q=stringstream&unscoped_q=stringstream

[dabonnie]

It doesn't look like this story is relevant anymore since there is no branching in any code using stringstream.
https://github.com/ros-tooling/system_metrics_collector/search?q=stringstream&unscoped_q=stringstream

Updated description, should be istringstream handling.