Minor code cleanups

[Thorium]

Minor code cleanups.

Copilot generated text-wall:
This pull request introduces several improvements and bug fixes across the codebase, with a focus on more robust type inference, performance and correctness in HTML parsing, and better error handling. The most important changes are summarized below:

HTML Parsing Improvements:

• Refactored the descendantsBy function in HtmlOperations.fs to use an explicit stack for traversing nodes, improving performance and avoiding stack overflows for deeply nested HTML. The traversal is now pre-order and processes children in document order.
• Updated the hasName function to use a case-insensitive comparison (StringComparison.OrdinalIgnoreCase) for matching node names, ensuring more robust HTML parsing regardless of case.

General Robustness and Error Handling:

• Improved URI parsing in Helpers.fs by using String.IsNullOrWhiteSpace instead of a manual check, making URI validation more robust and readable.
• Enhanced error messages in JsonSchema.fs for invalid reference paths, providing more informative feedback when a reference path does not lead through a record.

Type Inference Enhancements:

• Added a new inferenceMode parameter to the InferColumnTypes method in CsvInference.fs, allowing more control over how types are inferred from CSV data.