fix(eventstore): precise decimal (#8527)

# Which Problems Are Solved

Float64 which was used for the event.Position field is [not precise in
go and gets rounded](https://github.com/golang/go/issues/47300). This
can lead to unprecies position tracking of events and therefore
projections especially on cockcoachdb as the position used there is a
big number.

example of a unprecies position:
exact: 1725257931223002628
float64: 1725257931223002624.000000

# How the Problems Are Solved

The float64 was replaced by
[github.com/jackc/pgx-shopspring-decimal](https://github.com/jackc/pgx-shopspring-decimal).

# Additional Changes

Correct behaviour of makefile for load tests.
Rename `latestSequence`-queries to `latestPosition`

internal/eventstore/search_query_test.go

@@ -116,10 +116,10 @@ func TestSearchQuerybuilderSetters(t *testing.T) {
 		{
 			name: "set columns",
 			args: args{
-				setters: []func(*SearchQueryBuilder) *SearchQueryBuilder{testSetColumns(ColumnsMaxSequence)},
+				setters: []func(*SearchQueryBuilder) *SearchQueryBuilder{testSetColumns(ColumnsMaxPosition)},
 			},
 			res: &SearchQueryBuilder{
-				columns: ColumnsMaxSequence,
+				columns: ColumnsMaxPosition,
 			},
 		},
 		{