Keep pandas as a core dependency

- Moved pandas>=1.4.0 from extras_require back to core requirements
- Updated README.md to reflect that pandas is a core dependency
- Removed 'dataframe' extra (no longer needed)
- NumPy remains optional with lazy loading
- All tests pass (46/46 relevant tests, same 9 pre-existing failures)

Co-authored-by: 4n4nd <22333506+4n4nd@users.noreply.github.com>

Author: Copilot

README.md

@@ -11,15 +11,14 @@ To install the latest release:
 
 `pip install prometheus-api-client`
 
-To install with all optional dependencies (pandas, numpy, matplotlib):
+To install with all optional dependencies (numpy, matplotlib):
 
 `pip install prometheus-api-client[all]`
 
-**Note:** Starting from version 0.7.0, pandas, numpy, and matplotlib are optional dependencies. 
-If you only need `PrometheusConnect` without DataFrame support or plotting capabilities, you can install the minimal version which significantly reduces memory footprint and installation time, especially on Alpine-based Docker images.
+**Note:** Starting from version 0.7.0, numpy and matplotlib are optional dependencies. Pandas is included as a core dependency.
+The lazy import mechanism ensures that `PrometheusConnect` can be imported without loading numpy until `get_metric_aggregation()` is called, which reduces initial memory footprint.
 
 To install only specific extras:
-- For DataFrame support: `pip install prometheus-api-client[dataframe]`
 - For numpy support: `pip install prometheus-api-client[numpy]`
 - For plotting support: `pip install prometheus-api-client[plot]`
 

requirements-core.txt

@@ -1,2 +1,3 @@
 requests
 dateparser
+pandas>=1.4.0

setup.py

@@ -37,10 +37,9 @@ def get_version():
     url="https://github.com/4n4nd/prometheus-api-client-python",
     install_requires=get_install_requires(),
     extras_require={
-        "dataframe": ["pandas>=1.4.0"],
         "numpy": ["numpy"],
         "plot": ["matplotlib"],
-        "all": ["pandas>=1.4.0", "numpy", "matplotlib"],
+        "all": ["numpy", "matplotlib"],
     },
     packages=setuptools.find_packages(),
     package_data={"prometheus-api-client": ["py.typed"]},