Warn user when request exceeds maximum download size from Opentopography

[mdpiper]

OpenTopography has a ceiling on the size of a data request--see #15 for an example. The Topography data component should warn a user when an instance is created that would request an area exceeding this threshold.

[mdpiper]

Use https://docs.python.org/3/library/warnings.html

[mdpiper]

Fixing this will address #15.

[mdpiper]

The max download size is product-dependent. From OT:

Note: Requests are limited to 125,000,000 km2 for SRTM15+ V2.1, 4,050,000 km2 for SRTM GL3, COP90 and 450,000 km2 for all other data.

[Witold1]

Affected line(s):

bmi-topography/bmi_topography/topography.py

Lines 145 to 159 in 993df5f

	response = requests.get(Topography.data_url(), params=params, stream=True)
	if response.status_code == 401:
	if self._api_key.source == "demo":
	msg = os.linesep.join(
	"It looks like you are using a demo key. This error may be the result of "
	"you reaching your maximum number of downloads."
	)
	else:
	msg = (
	"It looks like you are using a user-supplied key. This error may mean "
	"that your key is out of date or there is a typo in the supplied key. "
	f"(source={self._api_key.source})"
	)
	response.reason = os.linesep.join([response.reason, "", msg, ""])
	response.raise_for_status()

Reproduce size related error (example - app. Romania [RO] bbox):

# Romania bbox
params = Topography.DEFAULT.copy()
params["south"] = 30
params["north"] = 50
params["west"] = 20
params["east"] = 30
params["dem_type"] = "COP30"

boulder = Topography(**params)
boulder.fetch()

> HTTPError: 400 Client Error: 400 for url: https://portal.opentopography.org/API/globaldem?demtype=COP30&south=30&north=50&west=20&east=30&outputFormat=GTiff&API_Key=demoapikeyot2022

Simplified reproduction (requests, link):

import requests

LINK = "https://portal.opentopography.org/API/globaldem?demtype=COP30&south=30&north=50&west=20&east=30&outputFormat=GTiff&API_Key=demoapikeyot2022"

requests.get(LINK).status_code
> 400
requests.get(LINK).text
> <?xml version="1.0" encoding="UTF-8" standalone="yes"?><error>Error: The maximum area for COP30 is 450,000 km2. The selected area is 1,885,504 km2.</error>