Improve event handlers to use clientCapabilitiesHolder

- BSLTextDocumentService: Use clientCapabilitiesHolder with map chain instead of event params
- DiagnosticProvider: Remove redundant null filters in Optional chain (map handles nulls)
- Both use method references for cleaner code
- Follows established patterns in codebase (e.g., WorkDoneProgressHelper)

Co-authored-by: nixel2007 <1132840+nixel2007@users.noreply.github.com>

Author: Copilot

src/main/java/com/github/_1c_syntax/bsl/languageserver/BSLTextDocumentService.java

@@ -53,6 +53,7 @@
 import org.eclipse.lsp4j.CallHierarchyOutgoingCall;
 import org.eclipse.lsp4j.CallHierarchyOutgoingCallsParams;
 import org.eclipse.lsp4j.CallHierarchyPrepareParams;
+import org.eclipse.lsp4j.ClientCapabilities;
 import org.eclipse.lsp4j.CodeAction;
 import org.eclipse.lsp4j.CodeActionParams;
 import org.eclipse.lsp4j.CodeLens;
@@ -93,6 +94,7 @@
 import org.eclipse.lsp4j.SelectionRange;
 import org.eclipse.lsp4j.SelectionRangeParams;
 import org.eclipse.lsp4j.SymbolInformation;
+import org.eclipse.lsp4j.TextDocumentClientCapabilities;
 import org.eclipse.lsp4j.TextEdit;
 import org.eclipse.lsp4j.WorkspaceEdit;
 import org.eclipse.lsp4j.jsonrpc.messages.Either;
@@ -528,10 +530,10 @@ public void reset() {
    */
   @EventListener
   public void handleInitializeEvent(LanguageServerInitializeRequestReceivedEvent event) {
-    var capabilities = event.getParams().getCapabilities();
-    if (capabilities != null && capabilities.getTextDocument() != null) {
-      clientSupportsPullDiagnostics = capabilities.getTextDocument().getDiagnostic() != null;
-    }
+    clientSupportsPullDiagnostics = clientCapabilitiesHolder.getCapabilities()
+      .map(ClientCapabilities::getTextDocument)
+      .map(TextDocumentClientCapabilities::getDiagnostic)
+      .isPresent();
   }
 
   private void validate(DocumentContext documentContext) {

src/main/java/com/github/_1c_syntax/bsl/languageserver/providers/DiagnosticProvider.java

@@ -28,10 +28,13 @@
 import com.github._1c_syntax.bsl.languageserver.events.LanguageServerInitializeRequestReceivedEvent;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
+import org.eclipse.lsp4j.ClientCapabilities;
 import org.eclipse.lsp4j.Diagnostic;
+import org.eclipse.lsp4j.DiagnosticWorkspaceCapabilities;
 import org.eclipse.lsp4j.DocumentDiagnosticReport;
 import org.eclipse.lsp4j.PublishDiagnosticsParams;
 import org.eclipse.lsp4j.RelatedFullDocumentDiagnosticReport;
+import org.eclipse.lsp4j.WorkspaceClientCapabilities;
 import org.springframework.context.event.EventListener;
 import org.springframework.stereotype.Component;
 
@@ -102,12 +105,9 @@ public void publishEmptyDiagnosticList(DocumentContext documentContext) {
   @EventListener
   public void handleInitializeEvent(LanguageServerInitializeRequestReceivedEvent event) {
     clientSupportsRefresh = clientCapabilitiesHolder.getCapabilities()
-      .map(capabilities -> capabilities.getWorkspace())
-      .filter(workspace -> workspace != null)
-      .map(workspace -> workspace.getDiagnostics())
-      .filter(diagnostics -> diagnostics != null)
-      .map(diagnostics -> diagnostics.getRefreshSupport())
-      .filter(refreshSupport -> refreshSupport != null)
+      .map(ClientCapabilities::getWorkspace)
+      .map(WorkspaceClientCapabilities::getDiagnostics)
+      .map(DiagnosticWorkspaceCapabilities::getRefreshSupport)
       .orElse(false);
   }