fix: validate embeddings against fitted dimensions (closes #34)

[botbikamordehai2-sketch]

What

fit() records embedding_dimensions_ for every embedding array passed, but transform() never checks anything against it. As a result, mismatched embeddings are accepted silently, allowing:

• Wrong embedding width → result blocks have incompatible feature dimensions
• Wrong number of rows → blocks have differing heights, causing shape errors or silent row misalignment downstream
• Missing/extra embeddings → blocks are silently dropped or unexpected blocks appear

This leads to confusing failures far from the cause or, worse, incorrect computations.

Fix

Added _validate_embeddings() that checks, for each embedding passed to transform():

• The set of embedding keys/indices matches those recorded during fit
• Each embedding is a 2D array with a width equal to the fitted embedding_dimensions_
• Each embedding has a row count equal to the number of samples in X

If any check fails, an IncompatibleParamsError is raised with a clear message naming the specific mismatch.

Closes #34