fix(shutdown): do not shutdown immediately busy backends (#3543)

* fix(shutdown): do not shutdown immediately busy backends

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* chore(refactor): avoid duplicate functions

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* fix: multiplicative backoff for shutdown (#3547)

* multiplicative backoff for shutdown

Rather than always retry every two seconds, back off the shutdown attempt rate? 

Signed-off-by: Dave <dave@gray101.com>

* Update loader.go

Signed-off-by: Dave <dave@gray101.com>

* add clamp of 2 minutes

Signed-off-by: Dave Lee <dave@gray101.com>

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Signed-off-by: Dave <dave@gray101.com>
Signed-off-by: Dave Lee <dave@gray101.com>

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Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Signed-off-by: Dave <dave@gray101.com>
Signed-off-by: Dave Lee <dave@gray101.com>
Co-authored-by: Dave <dave@gray101.com>