Update .gitignore file and add a .geminiignore file (#923)

This adds some more patterns to `.gitignore` for some of the tools known
to be used by the TFQ developers. Although these sorts of common ignore
patterns are better put in an individual user's global gitignore file
(something that can be configured in git), it turns out that Gemini CLI
also reads the `.gitignore` to determine what files to ignore in a
project. Making the project `.gitignore` file more comprehensive thus
helps us use AI code assistants more effectively.

This commit also adds an initial `.geminiignore` file for Gemini CLI.
Gemini CLI reads `.gitignore` too, but `.geminiignore` takes precedence;
this is essential for un-ignoring files that shouldn't be committed to
git yet _should_ be visible to Gemini CLI.

Author: mhucka

.geminiignore

@@ -0,0 +1,9 @@
+# Summary: tell Gemini CLI it should (or should not) ignore certain files and
+# folders. Gemini CLI reads .gitignore too, but .geminiignore takes precedence
+# -- useful for un-ignoring files that shouldn't be committed to git yet should
+# be visible to Gemini CLI. (Note also a different file, .aiexclude, is read by
+# Gemini Code Assist.) See https://geminicli.com/docs/cli/gemini-ignore/.
+
+# Don't ignore the Bazel config files created by configure.sh.
+!.bazelrc
+!.tf_configure.bazelrc

.gitignore

@@ -24,11 +24,13 @@
 .idea/*
 *.iml
 
-# ignore cache
+# ignore caches
 *__pycache__/*
 *.cache/*
 *.ipynb_checkpoints*
 .ipynb_checkpoints
+.mypy_cache
+.pytest_cache
 
 # Mac only
 .DS_Store
@@ -53,8 +55,11 @@ venv/
 quantum_env/
 quantum_venv/
 
-# ignore emacs temp files
-*#
+# Ignore Emacs backup, checkpoint, and other files.
+.\#*
+\#*\#
+.git/COMMIT_EDITMSG
+TAGS
 
 # vscode
 .vscode/*