chore: simplify model loading

[mudler]

Description

This PR fixes

CGO_LDFLAGS="" go build -ldflags "-s -w -X "github.com/mudler/LocalAI/internal.Version=v2.21.1-41-g5488fc3b" -X "github.com/mudler/LocalAI/internal.Commit=5488fc3bc14598ffb36a2d98f0b66705b45ebe0c"" -tags "p2p" -o local-ai ./              
# github.com/mudler/LocalAI/core/backend                                                                               
core/backend/tokenize.go:14:14: undefined: GRPCModelOpts
core/backend/tokenize.go:19:10: undefined: modelOpts                                                                   
core/backend/tokenize.go:21:9: undefined: model.WithThreads 

Notes for Reviewers

This is a follow-up on #3693 as #3710 was depending on it

Signed commits

• Yes, I signed my commits.

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