chore: [SVLS-5973] fix span pointer flow control

[apiarian-datadog]

What does this PR do?

We are refactoring the dd-trace-py span pointer code to use Optional[...] returns instead of raise Exception(...) for flow control in DataDog/dd-trace-py#11353 . We are also switching all of the logged warnings that our customers cannot directly fix to debug.

Motivation

This needs to be merged and released before the dd-trace-py change is released.

Testing Guidelines

Unit and integration tests. Will also check in a live lambda setup.

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog
• This PR passes the integration tests (ask a Datadog member to run the tests)

[apiarian-datadog]

tested this by the test lambda rig with both the new tracer code and the old. works as expected.

[nhulston]

LGTM!