Internalize `StreamId`s by using pointers to a string pool

[IvoDD]

Is your feature request related to a problem? Please describe. Currently StreamIds can be quite large strings and in various places around the code we need to worry about performance of copying them. Also we frequently use the same string in many places leading to memory usage as well.

Describe the solution you'd like As @willdealtry suggests we can use a string pool for all symbol names and make the StreamId just be a pointer to that string pool. This will make copying StreamId and storing copies of StreamId much more efficient.

Additional context Slack thread here