[perf] Add a way to reuse the buffer in ReadAnalyzer

[mcbegamerxx954]

It would be a good way to reuse allocations when reading multiple small-ish jsons

[vcschapp]

@mcbegamerxx954 , thanks for posting this issue.

Can you give some more specifics about your use case? A full description would be useful, but some examples of what'd help me include:

1. What are you doing at a high-level?
2. How are you using bufjson within your workflow?
3. How are you handling the JSON content, i.e., are you doing zero-copy usage of the content bytes?
4. How big are your small-ish JSONs?
5. What kind of system are you building and what are the resource constraints? e.g., Are you latency constrained, throughput-constrained, memory constrained, etc.?
6. Can you share any performance data or benchmarking data?

Any details like those help me figure out what kind of changes are needed (if any) to make your use case as optimal as possible.

It doesn't have to be super-formal and it's not necessary to hit all 6 of those bullets above but as much detail as you can share would help!