fix(api): propagate version kwarg in Api.init_app (#119)

[jbbqqf]

Summary

Api.__init__ accepts a version argument (defaulting to "1.0"), but
Api.init_app() silently drops any version= supplied in kwargs. Other
swagger-info fields (title, description, terms_url, contact*,
license*, url_scheme) are already forwarded from kwargs onto self.*;
version was the missing one. Match the existing pattern.

Fixes #119.

Context

The bug has been around since init_app was introduced. Lazy
initialization is the recommended pattern when the Flask app isn't
available at construction time, so users who try

api = Api()                       # version="1.0" by default
api.init_app(app, version="2.0")  # silently dropped

end up with info.version: "1.0" in their generated Swagger document. There
is no warning, which makes it confusing — they can see title/description
take effect from the same call.

Changes

• flask_restx/api.py: add self.version = kwargs.get("version", self.version)
  in init_app, mirroring the existing self.title = kwargs.get(...) lines.
  Also document version in the init_app docstring (it was already
  documented on __init__).
• tests/test_api.py: regression test test_init_app_overrides_version
  that both checks api.version and the rendered /swagger.json
info.version.
• CHANGELOG.rst: 1.3.3 bug-fix entry.

Reproduce BEFORE/AFTER yourself (copy-paste)

# --- one-time setup ---
git clone https://github.com/python-restx/flask-restx.git /tmp/restx-119 && cd /tmp/restx-119
python3 -m venv .venv && . .venv/bin/activate
pip install -q -e ".[test]" tzdata

# --- BEFORE: origin/master, expect version="1.0" and the new test to fail ---
git checkout origin/master
python -c "
from flask import Flask
from flask_restx import Api
app = Flask(__name__)
api = Api(version='1.0')
api.init_app(app, version='2.5')
print('api.version =', api.version)
with app.test_client() as c:
    print('info.version =', c.get('/swagger.json').get_json()['info']['version'])
"
# Expected (BEFORE the fix):
#   api.version = 1.0
#   info.version = 1.0

# --- AFTER: this branch, expect version="2.5" ---
git fetch https://github.com/jbbqqf/flask-restx.git fix/119-init-app-version
git checkout FETCH_HEAD
python -c "
from flask import Flask
from flask_restx import Api
app = Flask(__name__)
api = Api(version='1.0')
api.init_app(app, version='2.5')
print('api.version =', api.version)
with app.test_client() as c:
    print('info.version =', c.get('/swagger.json').get_json()['info']['version'])
"
# Expected (AFTER the fix):
#   api.version = 2.5
#   info.version = 2.5

What I ran locally

$ pytest tests/test_api.py -v 2>&1 | tail -5
tests/test_api.py::APITest::test_specs_url PASSED
tests/test_api.py::APITest::test_url_scheme PASSED
============================== 29 passed in 0.06s ==============================

$ pytest tests/test_api.py -k "init_app_overrides_version" -v 2>&1 | tail -5
collected 29 items / 28 deselected / 1 selected
tests/test_api.py::APITest::test_init_app_overrides_version PASSED
======================= 1 passed, 28 deselected in 0.01s =======================

$ pytest -q --no-header 2>&1 | tail -2
FAILED tests/test_inputs.py::URLTest::test_check - Failed: DID NOT RAISE <class 'ValueError'>
1 failed, 1237 passed in 18.19s

The single failure (tests/test_inputs.py::URLTest::test_check) is
pre-existing on master and unrelated to this change — it depends on
http://this-domain-should-not-exist.com actually not resolving, which is
no longer true on the network where the suite ran.

Edge cases

#	Scenario	api init	init_app call	Expected api.version	Verified by
1	constructor sets non-default, init_app supplies new value	Api(version="1.0")	init_app(app, version="2.5")	"2.5"	new regression test
2	constructor sets non-default, init_app omits version	Api(version="3.0")	init_app(app) (no version)	"3.0" (unchanged)	existing tests + kwargs.get(..., self.version)
3	constructor uses default, init_app omits version	Api() (default "1.0")	init_app(app)	"1.0" (default preserved)	existing test_root_endpoint_lazy flow

Risk / blast radius

Single-line change in init_app. The new behaviour only affects users who
already pass version= to init_app — today that value is silently
dropped, so any pre-existing caller is either already not relying on
init_app to set it (no observable change), or actively wishing it worked
(now does). No public API signature changes; no existing test required
edits.

---

PR drafted with assistance from Claude Code (Anthropic). The change was
reviewed manually against flask-restx's source. The reproducer block
above is the one I used during development; reviewers can paste it
verbatim.