Enhance Makefile with 'format_diff' Option and Improved Readability (#7394)

### Description:

This PR introduces a new option format_diff to the existing Makefile.
This option allows us to apply the formatting tools (Black and isort)
only to the changed Python and ipynb files since the last commit. This
will make our development process more efficient as we only format the
codes that we modify. Along with this change, comments were added to
make the Makefile more understandable and maintainable.

### Issue:

N/A

### Dependencies:

Add dependency to black.

### Tag maintainer:

@baskaryan

### Twitter handle:

[kzk_maeda](https://twitter.com/kzk_maeda)

---------

Co-authored-by: Bagatur <baskaryan@gmail.com>

.github/CONTRIBUTING.md

@@ -95,6 +95,14 @@ To run formatting for this project:
 make format
 ```
 
+Additionally, you can run the formatter only on the files that have been modified in your current branch as compared to the master branch using the format_diff command:
+
+```bash
+make format_diff
+```
+
+This is especially useful when you have made changes to a subset of the project and want to ensure your changes are properly formatted without affecting the rest of the codebase.
+
 ### Linting
 
 Linting for this project is done via a combination of [Black](https://black.readthedocs.io/en/stable/), [isort](https://pycqa.github.io/isort/), [flake8](https://flake8.pycqa.org/en/latest/), and [mypy](http://mypy-lang.org/).
@@ -105,6 +113,14 @@ To run linting for this project:
 make lint
 ```
 
+In addition, you can run the linter only on the files that have been modified in your current branch as compared to the master branch using the lint_diff command:
+
+```bash
+make lint_diff
+```
+
+This can be very helpful when you've made changes to only certain parts of the project and want to ensure your changes meet the linting standards without having to check the entire codebase.
+
 We recognize linting can be annoying - if you do not want to do it, please contact a project maintainer, and they can help you with it. We do not want this to be a blocker for good code getting contributed.
 
 ### Coverage

Makefile

@@ -1,40 +1,20 @@
 .PHONY: all clean format lint test tests test_watch integration_tests docker_tests help extended_tests
 
+# Default target executed when no arguments are given to make.
 all: help
 
+######################
+# TESTING AND COVERAGE
+######################
+
+# Run unit tests and generate a coverage report.
 coverage:
 	poetry run pytest --cov \
 		--cov-config=.coveragerc \
 		--cov-report xml \
 		--cov-report term-missing:skip-covered
 
-clean: docs_clean
-
-docs_compile:
-	poetry run nbdoc_build --srcdir $(srcdir)
-
-docs_build:
-	cd docs && poetry run make html
-
-docs_clean:
-	cd docs && poetry run make clean
-
-docs_linkcheck:
-	poetry run linkchecker docs/_build/html/index.html
-
-format:
-	poetry run black .
-	poetry run ruff --select I --fix .
-
-PYTHON_FILES=.
-lint: PYTHON_FILES=.
-lint_diff: PYTHON_FILES=$(shell git diff --name-only --diff-filter=d master | grep -E '\.py$$')
-
-lint lint_diff:
-	poetry run mypy $(PYTHON_FILES)
-	poetry run black $(PYTHON_FILES) --check
-	poetry run ruff .
-
+# Define a variable for the test file path.
 TEST_FILE ?= tests/unit_tests/
 
 test:
@@ -56,6 +36,44 @@ docker_tests:
 	docker build -t my-langchain-image:test .
 	docker run --rm my-langchain-image:test
 
+######################
+# DOCUMENTATION
+######################
+
+docs_compile:
+	poetry run nbdoc_build --srcdir $(srcdir)
+
+docs_build:
+	cd docs && poetry run make html
+
+docs_clean:
+	cd docs && poetry run make clean
+
+docs_linkcheck:
+	poetry run linkchecker docs/_build/html/index.html
+
+######################
+# LINTING AND FORMATTING
+######################
+
+# Define a variable for Python and notebook files.
+PYTHON_FILES=.
+lint format: PYTHON_FILES=.
+lint_diff format_diff: PYTHON_FILES=$(shell git diff --name-only --diff-filter=d master | grep -E '\.py$$|\.ipynb$$')
+
+lint lint_diff:
+	poetry run mypy $(PYTHON_FILES)
+	poetry run black $(PYTHON_FILES) --check
+	poetry run ruff .
+
+format format_diff:
+	poetry run black $(PYTHON_FILES)
+	poetry run ruff --select I --fix $(PYTHON_FILES)
+
+######################
+# HELP
+######################
+
 help:
 	@echo '----'
 	@echo 'coverage                     - run unit tests and generate coverage report'