Fix DeprecationWarning when encoding StripeObject metadata (fixes #1651)

[praniketkw]

Fixes #1651

Why?

When updating metadata on resources like invoices, users encountered a DeprecationWarning even though they were using the public API correctly. The warning was triggered internally when the encoder checked for the deprecated stripe_id property on StripeObject instances. While the deprecation warning serves an important purpose for direct user access to stripe_id, it should not be shown for internal library usage.

What?

• Modified the _api_encode function in stripe/_encode.py to suppress DeprecationWarning when internally accessing the stripe_id property.
• Added warnings.catch_warnings() context managers around both the hasattr check and the property access to prevent warnings from bubbling up to users during internal encoding operations.
• Preserved the deprecation warning for direct user access to stripe_id while silencing it only for internal library usage.
• Updated tests to verify that no deprecation warnings are raised during encoding operations while maintaining all existing encoding behavior.
• The approach maintains the intended deprecation strategy while fixing the user experience issue where legitimate API usage triggered internal warnings.

[ramya-stripe]

@praniketkw Can you also update the PR description based on the new approach?

[praniketkw]

@ramya-stripe Done!

[ramya-stripe]

@praniketkw Thanks for your work on this. Can you update the PR description to reflect the final approach we have taken here?