Report AsyncFile handler failures to context

[Boulea7]

Motivation:

Fixes #5343.

Exceptions thrown by AsyncFile data or end handlers should be reported to the owning Context, matching existing Vert.x handler semantics and the maintainer guidance in the issue.

This change installs a context exception handler on the AsyncFile inbound buffer and adds regression coverage for both handler types.

Testing:

• mvn -pl vertx-core -Dtest=FileSystemTest#testAsyncFileHandlerFailuresAreReportedToContext test -B — 1 passed
• mvn -pl vertx-core -Dtest=FileSystemTest,InboundBufferTest test -B — 141 passed
• mvn -pl vertx-core -DskipTests verify -Pcheckstyle -B — passed; Spotless reported 0 files needing changes
• git diff --check origin/master...HEAD — passed

Before this split, an earlier broad local run was not fully green. It encountered two unrelated environment-sensitive failures outside the modified paths:

• NameResolverTest#testRotationalServerSelection: expected 127.0.0.4 but observed 127.0.0.3.
• Http1xTest#requestAbsNoPort: connection timeout to www.google.com:80.

These are not counted as passing tests. All 142 relevant test executions listed above passed on the current rebased commit.

Conformance:

AI assistance: OpenAI Codex assisted with implementation and testing.

[vietj]

can you make two contributions instead of one that makes 2 changes ?

[Boulea7]

Thanks, I'll split these into two separate contributions.