Add some missed contract annotations

Author: Siebrenvde

src/main/java/dev/siebrenvde/ntfy/message/attachment/Attachment.java

@@ -20,6 +20,7 @@ public sealed interface Attachment permits FileAttachment, UrlAttachment {
      * @return a url attachment
      * @see <a href="https://docs.ntfy.sh/publish/#attach-file-from-a-url">Attach file from a URL</a>
      */
+    @Contract(value = "_, _ -> new", pure = true)
     static UrlAttachment url(final String url, @Nullable final String fileName) {
         return new UrlAttachmentImpl(url, fileName);
     }
@@ -31,6 +32,7 @@ static UrlAttachment url(final String url, @Nullable final String fileName) {
      * @return a url attachment
      * @see <a href="https://docs.ntfy.sh/publish/#attach-file-from-a-url">Attach file from a URL</a>
      */
+    @Contract(value = "_ -> new", pure = true)
     static UrlAttachment url(final String url) {
         return new UrlAttachmentImpl(url, null);
     }
@@ -43,6 +45,7 @@ static UrlAttachment url(final String url) {
      * @return a file attachment
      * @see <a href="https://docs.ntfy.sh/publish/#attach-local-file">Attach local file</a>
      */
+    @Contract(value = "_, _ -> new", pure = true)
     static FileAttachment file(final Path file, @Nullable final String fileName) {
         return new FileAttachmentImpl(file, fileName);
     }
@@ -54,6 +57,7 @@ static FileAttachment file(final Path file, @Nullable final String fileName) {
      * @return a file attachment
      * @see <a href="https://docs.ntfy.sh/publish/#attach-local-file">Attach local file</a>
      */
+    @Contract(value = "_ -> new", pure = true)
     static FileAttachment file(final Path file) {
         return new FileAttachmentImpl(file, null);
     }

src/main/java/dev/siebrenvde/ntfy/response/ErrorResponse.java

@@ -1,6 +1,7 @@
 package dev.siebrenvde.ntfy.response;
 
 import org.jetbrains.annotations.ApiStatus;
+import org.jetbrains.annotations.Contract;
 import org.jspecify.annotations.Nullable;
 
 /**
@@ -11,21 +12,25 @@ public sealed interface ErrorResponse permits ErrorResponseImpl {
     /**
      * {@return the ntfy error code}
      */
+    @Contract(pure = true)
     int code();
 
     /**
      * {@return the HTTP error code}
      */
+    @Contract(pure = true)
     int http();
 
     /**
      * {@return a description of the error}
      */
+    @Contract(pure = true)
     String error();
 
     /**
      * {@return a link to the documentation that may explain the issue}
      */
+    @Contract(pure = true)
     @Nullable String link();
 
     @ApiStatus.Internal

src/main/java/dev/siebrenvde/ntfy/response/PublishResponse.java

@@ -1,6 +1,7 @@
 package dev.siebrenvde.ntfy.response;
 
 import org.jetbrains.annotations.ApiStatus;
+import org.jetbrains.annotations.Contract;
 import org.jspecify.annotations.Nullable;
 
 import java.time.Instant;
@@ -13,16 +14,19 @@ public sealed interface PublishResponse permits PublishResponseImpl {
     /**
      * {@return the message id}
      */
+    @Contract(pure = true)
     String id();
 
     /**
      * {@return the time at which the message was or will be published}
      */
+    @Contract(pure = true)
     Instant time();
 
     /**
      * {@return the time at which the message will be deleted, or <code>null</code> if caching is disabled}
      */
+    @Contract(pure = true)
     @Nullable Instant expires();
 
     @ApiStatus.Internal