fix: pin dependency versions and Python support range

[maan-iitd2]

What

Pin dependency versions and Python support range in setup.py / requirements.txt. No code changes.

Change	Reason
great_expectations>=0.18.9,<1.0	InGen uses the legacy ge.from_pandas(...).expect_* Dataset API, removed in GE 1.0. Unpinned, pip install can resolve a GE version that silently breaks every validation.
pandas>=2.2.2,<3.0	pandas 3.0 turns Copy-on-Write on by default and drops deprecated APIs ingen's formatters/readers use.
openpyxl>=3.1.0 (new)	ingen/reader/file_reader.py and ingen/writer/writer.py call pd.read_excel/to_excel(engine='openpyxl') directly, but pandas does not install openpyxl by default — this was a missing, implicit dependency.
setup.py: python_requires='>=3.9,<3.13'	numpy<2 (forced transitively by GE's legacy-API requirement) has no wheels for Python 3.13+, so an unconstrained install on 3.13+ falls into a from-source numpy build that needs a C compiler and fails with a confusing error. This makes pip reject it up front with a clear message.
setup.py: read_requirements()	open('requirements.txt').read().splitlines() fed every line — including the new comments above — straight into install_requires. Replaced with a small filter that skips blank lines and # comments.
setup.py: resolve_version()	The version string ships as the literal token {{VERSION_PLACEHOLDER}}, substituted by CI (.github/workflows/python-publish.yml) via sed at release time. Locally, the token is left as-is, which isn't a valid PEP 440 version and makes pip install -e . fail on a fresh checkout. Falls back to 0.0.0.dev0 when the token hasn't been substituted; the release path is untouched.

Testing

Built a from-scratch venv (Python 3.12, no pre-existing installs):

• Before this change, pip install -e . on main fails outright — the unresolved {{VERSION_PLACEHOLDER}} isn't a valid version string, so setuptools raises InvalidVersion during dependency resolution.
• After this change, pip install -e . succeeds cleanly.
• Full suite: 393 passed / 33 failed on unmodified main → 404 passed / 22 failed with this change — the version pins fix 11 pre-existing failures (test_common_formatters.py, test_merger.py) caused by dependency drift on unpinned installs. The remaining 22 failures are pre-existing environment issues unrelated to packaging (missing GPG binary, Windows file locks, live network calls in test_api_reader/test_aiohttp_retry) — same failures, same count, on both branches.
• Ran python -m ingen end-to-end against the fresh install (XML source → CSV output) to confirm the installed package actually runs.
• Also confirmed python_requires does its job: installing into a Python 3.14 venv fails immediately with Package 'ingen-lib' requires a different Python: 3.14.0 not in '<3.13,>=3.9' instead of a numpy build failure.