[1/7][multi-lora]: utils foundation — sample/adapter types, adapter yaml config, shared helpers, CLI flags and validation

[mathewjhan]

#1638

[gemini-code-assist]

Code Review

This pull request introduces multi-LoRA training support, adding configuration parsing, command-line arguments, helper utilities, and validation logic, along with corresponding unit tests. Feedback focuses on improving robustness, specifically by replacing assert statements with ValueError exceptions for argument validation to ensure compatibility with optimized Python environments. Additionally, suggestions include specifying an explicit file encoding when loading YAML configurations, using safer dictionary access methods to prevent potential KeyError or TypeError exceptions, and adding defensive checks to avoid division-by-zero errors.

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[yushengsu-thu]

Reviewed extensively on the umbrella PR #1638 (2xH200 E2E validated); layer verified independently (imports + fast suites green on this branch's own tree).