chore: remove IDE artifacts from version control

The repository had 9 `.idea/` files committed against intent,
totaling ~7.5 MB — dominated by `.idea/CopilotChatHistory.xml`
(7.4 MB of AI chat history). The previous `.gitignore` enumerated
`.idea/X.xml` entries piecemeal, which let other IDE files
(encodings.xml, misc.xml, vcs.xml, codeStyles/, etc.) slip in.

This commit:

- Replaces the piecemeal `.idea/X.xml` block with a blanket
  `.idea` ignore plus symmetric `out/` handling, mirroring
  the sister repo `lance-format/lance-spark`.
- Runs `git rm --cached` on all 9 tracked `.idea/` files.
  They remain on disk for local IntelliJ use but are no longer
  under version control.

IDE-level codestyle (`.idea/codeStyles/*.xml`) is removed
intentionally: the planned Spotless + google-java-format
adoption will be the single source of truth for formatting;
a separate IDE codestyle in git would diverge over time.

Author: Vova Kolmakov

.gitignore

@@ -4,13 +4,13 @@ target/
 !**/src/test/**/target/
 
 ### IntelliJ IDEA ###
-.idea/modules.xml
-.idea/jarRepositories.xml
-.idea/compiler.xml
-.idea/libraries/
+.idea
 *.iws
 *.iml
 *.ipr
+out/
+!**/src/main/**/out/
+!**/src/test/**/out/
 
 ### Eclipse ###
 .apt_generated