Add ConfigResolver with necessary tests

[ubaskota]

Issue #, if available:

Description of changes:

Implements ConfigResolver to resolve configuration values from multiple sources in precedence order. The resolver iterates through sources and returns the first non-None value found, along with the source name for provenance tracking. Returns (None, None) when no source provides a value.

Tests
Added unit tests covering:

• Single and multiple source resolution
• Source precedence ordering
• Unresolved value handling
• Tuple return format validation

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[jonathan343]

Thanks Ujjwal.

I left some minor comments and suggestions. However, my biggest concern with this PR is the approach for config resolver sharing.

1. It doesn't follow any of the approaches discussed in previous designs
2. In cases where multiple threads hit the function before the first result is cached, it will result in each building their own resolver which is unnecessary/duplicate work

[SamRemis]

Nit: this test is a bit odd to me; I'm not sure what's different about string values that makes them special. I'd think this would be more like "test_resolved_returns_different_types", then we test a string, an int, a bool, and whatever else.

These test make it look like string is the default type that a resolver will return, and I don't think that's true.