Stop the request pool pulling new work after a failure

[kmcginnes]

Description

• mapWithConcurrency rejected on the first failure, but its other lanes kept looping and sending requests nobody was waiting for. The first rejection now stops the pool from starting new work. Callbacks already running aren't cancelled.
• This also affects openCypher and SPARQL schema and edge connection fetches, which used to drain the whole queue after a failure.
• Later in the stack, edge connection discovery relies on this, so abandoning an attempt actually stops it.

Validation

• New test: after one callback rejects, no further callbacks start.
• pnpm checks and pnpm test clean on this layer.

Related Issues

• Part of [3.2.2][Gremlin] Relationship discovery fails with MemoryLimitExceededException for high-cardinality edge labels #2141 (split out of Ask the database for distinct edge connections instead of scanning edges #2244)
• Layer 1 of 6. Stack, bottom first: Stop the request pool pulling new work after a failure #2281 → Show the Schema view without edge connections when their discovery fails #2277 → Put the advanced connection settings behind a disclosure #2278 → Sample each edge type with its own limit, 10 types per request #2279 → Ask the database for distinct edge connections instead of scanning edges #2280 → Let a connection choose how edge connections are discovered #2282

Check List

• I confirm that my contribution is made under the terms of the Apache 2.0 license.
• I have verified pnpm checks passes with no errors.
• I have verified pnpm test passes with no failures.
• I have covered new added functionality with unit tests if necessary.
• I have updated documentation if necessary.