feat: land remaining #290–#328 stack features onto main

[seonghobae]

Summary

• Lands the full remaining Add Thurstone (1927) Case V paired-comparison scaling #290–Add sample size for Cohen's kappa (irr N.cohen.kappa) #328 seonghobae stack tip (seonghobae-ncohen) onto current main: paired-comparison scaling, rating systems, and inter-rater reliability/agreement APIs + tests.
• Add Thurstone (1927) Case V paired-comparison scaling #290 (Thurstone) already squash-merged to main. Intermediate stack PRs could not retarget cleanly after squash (DIRTY/CONFLICTING) and some were incorrectly mergeable only into non-main bases; this PR is the intentional main-landing integration.
• Preserves main GPU/MT NLL (lib.rs / NLL_MT_PERSON_FLOOR / wgpu path unchanged).

Supersedes / closes chain members

Closes remaining open stack PRs once this merges (or supersedes their content):
#291 #293 #295 #297 #301 #303 #305 #307 #309 #313 #317 #318 #319 #320 #321 #325 #326 #327 #328
(Plus notes for side-base merges that never landed on main: #292 #294 #296 #298 #302 #304 #306 #308 #311.)

Test plan

• cargo test -p mlsirm-core --lib -- scaling:: (111 passed locally)
• CI full suite on this PR
• Confirm GPU/MT symbols remain on main after merge

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📥 Commits

Reviewing files that changed from the base of the PR and between 853de10 and 9a9cb35.

📒 Files selected for processing (13)

• CHANGELOG.md
• crates/fast-mlsirm-py/src/lib.rs
• crates/mlsirm-core/src/agreement.rs
• crates/mlsirm-core/src/reliability.rs
• crates/mlsirm-core/src/scaling.rs
• python/fast_mlsirm/__init__.py
• python/fast_mlsirm/reliability.py
• python/fast_mlsirm/scaling.py
• python/fast_mlsirm/validation.py
• tests/test_paper_features.py
• tests/unit/agreement_tests.rs
• tests/unit/reliability_tests.rs
• tests/unit/scaling_tests.rs

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