fix: Only strip config key prefix when present

[kylebarron]

Problem

IntoPyObject for the S3/GCS/Azure config keys assumed every key as_ref()s to a prefixed string, and used .expect() to strip it:

self.0.as_ref().strip_prefix("aws_").expect("Expected config prefix to start with aws_")

But object_store delegates client and encryption keys to inner enums — Self::Client(opt) => opt.as_ref(), Self::Encryption(opt) => opt.as_ref() — which return unprefixed names like allow_http. So reading .config on a store built with any client option panicked:

>>> S3Store("bucket", allow_http=True).config
pyo3_runtime.PanicException: Expected config prefix to start with aws_

All three stores were affected (aws_, google_, azure_).

Fix

Strip the prefix only when it's actually present, matching what object_store's own FromStr does (s.strip_prefix("aws_").unwrap_or(s)).

Also: aws_endpoint_url_s3 round-trip

While auditing every config key across the three stores for the same asymmetry, aws_endpoint_url_s3 turned out to be the only key with no unprefixed alias upstream — from_str accepts aws_endpoint_url_s3 but not endpoint_url_s3, unlike its sibling endpoint_url_sts which has both. Since we emit keys unprefixed, the value we produced couldn't be fed back in:

>>> store = S3Store("bucket", aws_endpoint_url_s3="https://example.com")
>>> store.config
{'bucket': 'bucket', 'endpoint_url_s3': 'https://example.com'}
>>> pickle.loads(pickle.dumps(store))
UnknownConfigurationKeyError: Configuration key: 'endpoint_url_s3' is not valid for store 'S3'

PyAmazonS3ConfigKey::extract now retries the parse with an aws_ prefix on failure. Worth an upstream PR adding the missing alias too.

Testing

Regression tests added for each store. I also scanned every config key alias in all three stores for these two failure modes; no others remain.

Note

Found while investigating #753. This does not fix that issue — AWS_ENDPOINT_URL_S3 beating an explicit endpoint= kwarg is a separate problem (Endpoint and S3Endpoint are distinct upstream keys, and build() does self.s3_endpoint.or(self.endpoint) unconditionally). It does, however, make the aws_endpoint_url_s3= workaround usable with .config/pickling.

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