Rethink Watch #128
Description
TL:DR; Replace watch() with incremental read() polling
Why
The current implementation of watch() is complex to implement in providers and doesn't support back-pressure or resumption.
Steps
- Implement the new where query version semantics ("if-changed-after")
- Specify that version is a non-negative number, and that version 0 has a special meaning
- Implement the querying of linked paths in graffy-link and drop graffy-fill completely
- Restrict the use of finalize() to queries with version 0 in core, pg and link
- Implement query version filtering in slice(): exclude unchanged from both known and unknown
- Implement query version filtering in pg by adding a condition on verCol
- Implement the async iterator form of read() to perform incremental polling