feat: auto-register ObjectStore and accept it in read/register methods

Closes #899. Users no longer need to call `register_object_store()`
before reading remote files. Two complementary mechanisms are provided:

**Auto-registration from URL scheme**
`try_register_url_store()` is called inside every `read_*` /
`register_*` method. It parses the path, detects the scheme (s3, gs,
az/abfss, http/https) and builds an appropriate `ObjectStore` from
environment variables. An existing registration is never overwritten, so
an explicit `register_object_store()` call still takes precedence.
Anonymous S3 access is enabled via `AWS_SKIP_SIGNATURE=true/1`
(avoids EC2 IMDS timeouts when not running on AWS).

**`object_store` parameter on read/register methods**
All eight `read_*` / `register_*` methods (`read_parquet`,
`register_parquet`, `read_csv`, `register_csv`, `read_json`,
`register_json`, `read_avro`, `register_avro`) now accept an optional
`object_store` keyword argument. Passing a store instance registers it
for the URL immediately, with no separate call required:

```python
from datafusion.object_store import S3Store
store = S3Store("my-bucket", region="us-east-1", skip_signature=True)
df = ctx.read_parquet("s3://my-bucket/data.parquet", object_store=store)
```

**pyo3-object-store integration**
Replaced the hand-rolled `store.rs` Python classes with
`pyo3-object_store 0.9` (compatible with object_store 0.13), which
provides richer, actively maintained Python builders for every backend.
The `datafusion.object_store` module now exposes `S3Store`, `GCSStore`,
`AzureStore`, `HTTPStore`, `LocalStore`, `MemoryStore`, and `from_url`.
Legacy names (`AmazonS3`, `GoogleCloud`, `MicrosoftAzure`, `Http`,
`LocalFileSystem`) are kept as backward-compatible aliases.

`register_object_store(url, store)` now takes a full URL prefix and a
`PyObjectStore` instead of the old `(scheme, StorageContexts, host)`
triple, matching the pattern suggested in #899.

**Tests**
Added integration tests (`@pytest.mark.integration`):
- `test_read_http_csv` - reads CSV from GitHub raw HTTPS
- `test_read_https_parquet` - reads Parquet from Apache parquet-testing
- `test_read_s3_parquet_explicit` - passes `S3Store` via `object_store=`
- `test_read_s3_parquet_auto` - uses `AWS_SKIP_SIGNATURE=true` env var

Author: mesejo

Cargo.lock

@@ -56,6 +56,7 @@ async-trait = "0.1.89"
 futures = "0.3"
 cstr = "0.2"
 object_store = { version = "0.13.1" }
+pyo3-object_store = { version = "0.9" }
 url = "2"
 log = "0.4.29"
 parking_lot = "0.12"

Cargo.toml

@@ -63,6 +63,7 @@ async-trait = { workspace = true }
 futures = { workspace = true }
 cstr = { workspace = true }
 object_store = { workspace = true, features = ["aws", "gcp", "azure", "http"] }
+pyo3-object_store = { workspace = true }
 url = { workspace = true }
 log = { workspace = true }
 parking_lot = { workspace = true }