Improve Coderabbit config with .coderabbit.yaml (#955)

Address @nene's feedback in
#947 (comment)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Chores**
* Updated code review tool configuration settings (including review and
chat features) to better control the format and focus of automated
assistance.

**Note:** This release contains no user-facing changes.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: nene

.coderabbit.yaml

@@ -0,0 +1,16 @@
+# yaml-language-server: $schema=https://coderabbit.ai/integrations/schema.v2.json
+reviews:
+  # Add summary to walkthrough instead of PR description
+  high_level_summary_in_walkthrough: true
+  # Disable useless fortune
+  in_progress_fortune: false
+  # Disable useless poem
+  poem: false
+  pre_merge_checks:
+    # Disable useless docstrings checks
+    docstrings:
+      mode: disabled
+
+chat:
+  # Disable useless ASCII art or emojis in chat responses
+  art: false