fix: random seed controls splitting

[stephantul]

This PR adds a random seed to control splitting behavior

[greptile-apps]

Confidence Score: 5/5

[Medium impact] The PR appears safe to merge; no actionable issues were found.

_{Reviews (1) · Last reviewed commit: "fix: random seed controls splitting" · Reviewed by Greptile}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
model2vec/train/base.py	100.00% <ø> (ø)
model2vec/train/classifier.py	100.00% <ø> (ø)
model2vec/train/pairs.py	100.00% <100.00%> (ø)
model2vec/train/similarity.py	100.00% <100.00%> (ø)
model2vec/train/utils.py	100.00% <100.00%> (ø)

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