[Python SDK] Restrict tag size

[selcukcihan]

Description

• Related issue https://linear.app/serverless/issue/SC-1129/sdk-field-size-limits#comment-6fef104d
• Restrict tag name to max 256 characters and tag value to 32766 bytes
• Ensure error.message and error.stacktrace are truncated to fit the limit
• Fix handling of lists for tag values, make sure lists are flat

Testing done

Unit & integration tested

[selcukcihan]

@medikoo ready for review 🙏