[improve][pip] PIP-396: Align WindowFunction's WindowContext with BaseContext

pip/pip-396.md

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+# PIP-396: Align WindowFunction's WindowContext with BaseContext
+
+# Background knowledge
+
+Pulsar Functions and Connectors provide a `BaseContext` object, enabling users to access the current execution environment, including logs, metrics, states, secrets, and other context-specific features.  
+The `WindowFunction`, designed to process multiple messages at once, offers a `WindowContext` object with similar functionality. However, `WindowContext` lacks certain features available in `BaseContext`.
+
+# Motivation
+
+Currently, the `WindowContext` interface does not include some critical methods provided by `BaseContext`, such as `getSecret` and `deleteState`. This limitation makes Window Functions feel less capable compared to standard Functions.
+
+# Goals
+
+## In Scope
+
+- Enhance `WindowContext` by adding missing features from `BaseContext`.
+
+## Out of Scope
+
+# High-Level Design
+
+The solution involves aligning `WindowContext` with `BaseContext` by extending the `WindowContext` interface and implementing missing methods in `WindowContextImpl`.
+
+# Detailed Design
+
+## Design & Implementation Details
+
+Refer to implementation PR: https://github.com/apache/pulsar/pull/23628
+
+The implementation strategy is straightforward:
+
+- Update the `WindowContext` interface to extend the `BaseContext` interface.
+- Remove duplicate method definitions in `WindowContext` already covered by `BaseContext`.
+- Implement the following missing methods in the `WindowContextImpl` class:
+
+```java
+@Override
+public String getSecret(String secretName) {
+    return this.context.getSecret(secretName);
+}
+
+@Override
+public CompletableFuture<Void> incrCounterAsync(String key, long amount) {
+    return this.context.incrCounterAsync(key, amount);
+}
+
+@Override
+public CompletableFuture<Long> getCounterAsync(String key) {
+    return this.context.getCounterAsync(key);
+}
+
+@Override
+public CompletableFuture<Void> putStateAsync(String key, ByteBuffer value) {
+    return this.context.putStateAsync(key, value);
+}
+
+@Override
+public CompletableFuture<ByteBuffer> getStateAsync(String key) {
+    return this.context.getStateAsync(key);
+}
+
+@Override
+public void deleteState(String key) {
+    this.context.deleteState(key);
+}
+
+@Override
+public CompletableFuture<Void> deleteStateAsync(String key) {
+    return this.context.deleteStateAsync(key);
+}
+
+@Override
+public void fatal(Throwable t) {
+    this.context.fatal(t);
+}
+```
+
+## Public-facing Changes
+
+With this update, developers working on Window Functions can leverage the following new methods from WindowContext:
+
+- getSecret
+- incrCounterAsync
+- getCounterAsync
+- putStateAsync
+- getStateAsync
+- deleteState
+- deleteStateAsync
+- fatal
+
+### Configuration
+
+# Backward & Forward Compatibility
+
+This update is fully backward-compatible. No existing methods in WindowContext are modified or removed, ensuring seamless integration with current implementations.