eth/filters: honor context cancellation in bor block-log range scan

[lucca30]

What

BorBlockLogsFilter.unindexedLogs scans a block range one sprint at a time but
never checked the request context, so a request whose context was cancelled —
the client disconnected, or a deadline fired — kept scanning the full range and
held its RPC worker until the range was exhausted.

Upstream go-ethereum performs this check at the top of its unindexedLogs loop
(eth/filters/filter.go); the bor block-log filter omitted it.

Change

Restore parity with a select { case <-ctx.Done(): ... } guard at the top of
the loop, so a range scan stops promptly once the caller is gone. With the
context now observed, any deadline attached upstream (e.g. an operator-configured
RPC timeout) also bounds the scan.

Why

Without the check, a long range query keeps consuming a worker after its result
can no longer be delivered, reducing the RPC server's effective capacity under
cancelled or abandoned requests. The fix is small and matches the canonical
go-ethereum loop.

Changes

• eth/filters/bor_filter.go: add the context-cancellation check to the
  unindexedLogs scan loop.
• eth/filters/bor_filter_test.go: add TestBorFilterHonorsContextCancellation
  and TestBorFilterHonorsContextDeadline.

Testing

• go test ./eth/filters/ — all pass (28).
• The new tests fail on the prior code (the loop ran 1001 block reads on an
  already-cancelled context and returned a nil error) and pass with the fix.

[sonarqubecloud]

Quality Gate failed

Failed conditions
38.7% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 53.40%. Comparing base (706b800) to head (01f3bff).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2259      +/-   ##
===========================================
- Coverage    53.41%   53.40%   -0.02%     
===========================================
  Files          896      896              
  Lines       159713   159721       +8     
===========================================
- Hits         85314    85302      -12     
- Misses       69071    69090      +19     
- Partials      5328     5329       +1     

Files with missing lines	Coverage Δ
eth/filters/bor_filter.go	80.21% <100.00%> (+1.90%)	⬆️

... and 16 files with indirect coverage changes

Files with missing lines	Coverage Δ
eth/filters/bor_filter.go	80.21% <100.00%> (+1.90%)	⬆️

... and 16 files with indirect coverage changes

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