#27989 Add bounds validation for LinearClassifier coefficients

Description

Add input validation to the LinearClassifier operator to prevent an out-of-bounds heap read in GEMM when a crafted model provides mismatched coefficients/intercepts sizes.

Fixes https://portal.microsofticm.com/imp/v5/incidents/details/31000000559851/summary

Changes

• Constructor: Validate class_count_ > 0 and coefficients_.size() % class_count_ == 0
• Compute(): Validate coefficients_.size() == class_count * num_features before GEMM call
• Tests: Two regression tests for invalid coefficient sizes

Motivation and Context

MSRC case 109185 (VULN-176698): OOB read via GEMM from crafted model in LinearClassifier operator. Root cause is missing validation that the coefficients vector size matches [class_count, num_features] before passing raw pointers to GEMM.