Small improvements of CSndLossList::insert

[maxsharabayko]

1. Added several unit tests.
2. Minor refactoring of the CSndLossList::insert(..).
3. Improved CSndLossList::insert(..) for the serial element.

Example of the improvement. Three insert operations:

insert(1, 2);
insert(4, 4);
insert(3, 3);

The state of the list after every insert operation was (format pos:[seqstart, seqend]):

0:[1, 2]
0:[1, 2], 3:[4]
0:[1, 2], 2:[3], 3:[4]

After this PR:

0:[1, 2], 
0:[1, 2], 3:[4] 
0:[1, 4] 

Taken from TEST_F(CSndLossListTest, InsertCoalesce)

[ethouris]

It would be better to use LOG* facility to display it. Even if this is only left for future debugging.

Of course, you'd need std::ostringstream for intermediate collection, as a single log instruction cannot print a fragment of a line.

[maxsharabayko]

Can LOGF not end the line with \n like Verb() allows to do?

[ethouris]

Unfortunately not. One log instruction always ends with an end of line. Partial-line logging would have to be added support.

[maxsharabayko]

Then would be simpler to leave this type of output for the sake of code simplicity.

[ethouris]

Verb() has a special VerbNoEOL tag to leave without EOL. But Verb() doesn't have a log header, so there's a little problem with this. For LOG* we'd need something like a temporary log cumulation variable, which will be then reused when doing a final log with EOL. But I don't think we could this way do any better than by using std::ostringstream.