Fix dead code in IndexConfigBuilder::build() logic, and other issues

[hpdic]

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Reference Issues/PRs

What does this implement/fix? Briefly explain your changes.

This PR fixes a logical error in IndexConfigBuilder::build() where a safety check logic was duplicated, causing the logging code to become unreachable dead code. A couple of minor things: missing some header includes; string check is redundant.

Previously, there were two identical if (_dynamic_index && _num_frozen_pts == 0) checks.

The first check silently set _num_frozen_pts = 1.

The second check (which contained the warning log) would effectively become if (true && 1 == 0), which always evaluates to false.

As a result, the warning message "_num_frozen_pts passed as 0 ..." would never be printed.

The fix: I removed the first redundant check. Now the code correctly logs the warning before overriding the value to 1.

I also fixed a few other minor things like missing header includes and string checks.

Any other comments?

[Copilot]

Pull request overview

Fixes unreachable/dead warning logic in IndexConfigBuilder::build() by removing a duplicated safety check so the _num_frozen_pts == 0 warning is emitted before clamping the value for dynamic indexes. Also makes the header more self-contained by adding missing includes and simplifies a redundant string emptiness check.

Changes:

• Remove the duplicated if (_dynamic_index && _num_frozen_pts == 0) that previously made the warning branch unreachable.
• Add missing header includes needed for types used in index_config.h (e.g., std::shared_ptr, std::string, Metric, ANNException, diskann::cout).
• Simplify _data_type validation from == "" || empty() to empty().

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