chore: Log interrupted exception, address comment todo. (#131)

<!-- CURSOR_SUMMARY -->
> [!NOTE]
> **Low Risk**
> Behavioral changes are limited to logging and minor exception-handling
semantics in polling code; low risk aside from potentially changing how
shutdown-related interrupts propagate.
> 
> **Overview**
> Improves polling robustness/observability by making
`PollingBase.logger` `protected` for subclasses and clarifying that
failures while translating a changeset are treated as *invalid data*.
> 
> Updates `PollingSynchronizerImpl` to handle `InterruptedException` and
`ExecutionException` separately, emitting debug logs and restoring the
thread interrupt flag when interrupted.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
5d0ff6e. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: kinyoklion

lib/sdk/server/src/main/java/com/launchdarkly/sdk/server/PollingBase.java

@@ -17,7 +17,7 @@
 
 class PollingBase {
     private final FDv2Requestor requestor;
-    private final LDLogger logger;
+    protected final LDLogger logger;
 
     public PollingBase(FDv2Requestor requestor, LDLogger logger) {
         this.requestor = requestor;
@@ -119,7 +119,8 @@ protected CompletableFuture<FDv2SourceResult> poll(Selector selector, boolean on
                             );
                             return FDv2SourceResult.changeSet(converted, fdv1Fallback);
                         } catch (Exception e) {
-                            // TODO: Do we need to be more specific about the exception type here?
+                            // Whatever exception happened here means we couldn't handle the data. So we are going to
+                            // treat that as invalid data.
                             DataSourceStatusProvider.ErrorInfo info = new DataSourceStatusProvider.ErrorInfo(
                                     DataSourceStatusProvider.ErrorKind.INVALID_DATA,
                                     0,

lib/sdk/server/src/main/java/com/launchdarkly/sdk/server/PollingSynchronizerImpl.java

@@ -71,8 +71,14 @@ private void doPoll() {
             } else {
                 resultQueue.put(res);
             }
-        } catch (InterruptedException | ExecutionException e) {
-            // TODO: Determine if handling is needed.
+        } catch (InterruptedException e) {
+            // This would likely be the result of a shutdown, so we are just logging this for debugging purposes.
+            // Same with the ExecutionException below.
+            logger.debug("Polling thread interrupted: {}", e.toString());
+            Thread.currentThread().interrupt();
+        }
+        catch(ExecutionException e) {
+            logger.debug("Polling thread execution exception: {}", e.toString());
         }
     }