mitigate model load diff calculation issues on neptune

[dlamoris]

During model load diff generation at https://github.com/Open-MBEE/flexo-mms-layer1-service/blob/v0.1.1/src/main/kotlin/org/openmbee/flexo/mms/routes/gsp/ModelLoad.kt#L220, ?srcGraph as a var can cause neptune to stall.
Example:

PREFIXES...
insert {
    graph m-graph:Transactions {
        mt:diff a mms:Transaction ;
            mms:created "2024-01-23T02:51:56.654793433Z"^^<http://www.w3.org/2001/XMLSchema#dateTime> ;
            mms:serviceId "mms5-layer1-0" ;
            mms:requestPath "/orgs/jama/repos/msr3/branches/master/graph" ;
            mms:requestMethod "POST" ;
            mms:authMethod ?__mms_authMethod ;
            mms:appliedGroupId ?__mms_groupId ;
            # mms:requestBody "" ;
            mms:requestBodyContentType "text/turtle" ;
            mms-txn:srcGraph ?srcGraph ;
            mms-txn:dstGraph mor-graph:Load.53b47e3b-4b6c-4044-a03f-ee721496770f ;
            mms-txn:insGraph ?insGraph ;
            mms-txn:delGraph ?delGraph ;
            mms:user mu: ;
            mms:org mo: ;
            mms:repo mor: ;
            mms:branch morb: ;
    
            .
    }
    graph m-graph:AccessControl.Policies {
        m-policy:AutoDiffOwner.6b6cda4d-8528-44d0-bb6c-439fc23e88aa a mms:Policy ;
            mms:subject mu: ;
            mms:scope mord: ;
            mms:role mms-object:Role.AdminDiff  ;
            .
    
    }
    graph ?insGraph {
        ?ins_s ?ins_p ?ins_o .    
    }
    
    graph ?delGraph {
        ?del_s ?del_p ?del_o .
    }
    
    graph mor-graph:Metadata {
        ?diff a mms:Diff ;
            mms:id ?diffId ;
            mms:createdBy mu: ;
            mms:srcCommit ?srcCommit ;
            mms:dstCommit <https://mms5.jpl.nasa.gov/orgs/jama/repos/msr3/commits/53b47e3b-4b6c-4044-a03f-ee721496770f> ;
            mms:insGraph ?insGraph ;
            mms:delGraph ?delGraph ;
            .
    }
    
    
    
}
where {
    graph mor-graph:Metadata {
            # select the latest commit from the current named ref
            mor-branch:master mms:commit ?srcCommit .
    
            # get the latest snapshot associated with the source commit
            ?srcCommit ^mms:commit/mms:snapshot ?srcSnapshot .
            {
                # prefer the model snapshot
                ?srcSnapshot a mms:Model ;
                    mms:graph ?srcGraph  .
            } union {
                # settle for staging...
                ?srcSnapshot a mms:Staging ;
                    mms:graph ?srcGraph .
    
                # ...if model is not available
                filter not exists {
                    ?srcCommit ^mms:commit/mms:snapshot/a mms:Model .
                }
            }
        }
    
    
    bind(
        sha256(
            concat(str(<https://mms5.jpl.nasa.gov/orgs/jama/repos/msr3/commits/53b47e3b-4b6c-4044-a03f-ee721496770f>), "\n", str(?srcCommit))
        ) as ?diffId
    )
    
    bind(
        iri(
            concat(str(<https://mms5.jpl.nasa.gov/orgs/jama/repos/msr3/commits/53b47e3b-4b6c-4044-a03f-ee721496770f>), "/diffs/", ?diffId)
        ) as ?diff
    )
    
    bind(
        iri(
            concat(str(mor-graph:), "Diff.Ins.", ?diffId)
        ) as ?insGraph
    )
    
    bind(
        iri(
            concat(str(mor-graph:), "Diff.Del.", ?diffId)
        ) as ?delGraph
    )
    
    
    {
        # delete every triple from the source graph...
        graph ?srcGraph {
            ?del_s ?del_p ?del_o .
        }
    
        # ... that isn't in the destination graph 
        filter not exists {
            graph mor-graph:Load.53b47e3b-4b6c-4044-a03f-ee721496770f {
                ?del_s ?del_p ?del_o .
            }
        }
    } union {
        # insert every triple from the destination graph...
        graph mor-graph:Load.53b47e3b-4b6c-4044-a03f-ee721496770f {
            ?ins_s ?ins_p ?ins_o .
        }
    
        # ... that isn't in the source graph
        filter not exists {
            graph ?srcGraph {
                ?ins_s ?ins_p ?ins_o .
            }
        }
    } union {}
}

This can cause Neptune to think for 30 min and times out

Replacing ?srcGraph with a definite graph lets the update finish in under 2 minutes

I think we'll have to do something similar to model query where the srcGraph is queried first.