chore(sdk-examples): update examples and description for python SDK v14.1.0 (#2499)

* chore(sdk-examples): fix broken Python SDK imports

Two stellar_sdk (py-stellar-base, current 14.1.0) imports reference
names that do not exist and raise ImportError at runtime:

- working-with-contract-specs.mdx: `from stellar_sdk import ... stellar_xdr`
  — there is no top-level `stellar_xdr` export. The code uses
  `stellar_xdr.SCVal.from_xdr(...)`, so import the `xdr` submodule under
  that alias (`xdr as stellar_xdr`), matching the pattern used in the
  sibling invoke-contract-tx-sdk guide.
- data-format/xdr.mdx: `import xdr from stellar_sdk;` is JS-style syntax;
  corrected to `from stellar_sdk import xdr`.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* chore(sdk-examples): correct py-stellar-base minimum Python version

py-stellar-base now requires Python >=3.10,<4.0 (pyproject.toml
`requires-python`), but the client-sdks page still stated "Python 3.7+
as well as PyPy 3.7+". Update to 3.10+ to match the current release.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ElliotFriend

docs/build/guides/dapps/working-with-contract-specs.mdx

@@ -1240,7 +1240,7 @@ env.events()
 ```
 
 ```python
-from stellar_sdk import SorobanServer, scval, stellar_xdr
+from stellar_sdk import SorobanServer, scval, xdr as stellar_xdr
 from stellar_sdk.exceptions import NotFoundError, BadResponseError
 from stellar_sdk.soroban_server import EventFilter, EventFilterType
 

docs/learn/fundamentals/data-format/xdr.mdx

@@ -63,7 +63,7 @@ You can see the full set of options to construct a `Uint64` in the definition fo
 Other languages, such as Python (see `stellar-sdk`'s [uint64.html](https://stellar-sdk.readthedocs.io/en/stable/_modules/stellar_sdk/xdr/uint64.html) documentation), support arbitrarily-sized integers by default, so there are no such variations:
 
 ```python
-import xdr from stellar_sdk;
+from stellar_sdk import xdr
 
 u64 = xdr.Uint64(1_000_000_000_000_000)
 ```

docs/tools/sdks/client-sdks.mdx

@@ -38,7 +38,7 @@ It provides:
 
 **The Python SDK is maintained by dedicated community developers.**
 
-`py-stellar-base` is a Python library for communicating with a Stellar Horizon server. It is used for building Stellar apps on Python. It supports Python 3.7+ as well as PyPy 3.7+.
+`py-stellar-base` is a Python library for communicating with a Stellar Horizon server. It is used for building Stellar apps on Python. It supports Python 3.10+ as well as PyPy 3.10+.
 
 This SDK is maintained by a dedicated community developer.