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/v2/system/mirror/succeeded.go

@@ -1,6 +1,8 @@
 package mirror
 
 import (
+	"github.com/shopspring/decimal"
+
 	"github.com/zitadel/zitadel/internal/v2/eventstore"
 	"github.com/zitadel/zitadel/internal/zerrors"
 )
@@ -9,7 +11,7 @@ type succeededPayload struct {
 	// Source is the name of the database data are mirrored from
 	Source string `json:"source"`
 	// Position until data will be mirrored
-	Position float64 `json:"position"`
+	Position decimal.Decimal `json:"position"`
 }
 
 const SucceededType = eventTypePrefix + "succeeded"
@@ -38,7 +40,7 @@ func SucceededEventFromStorage(event *eventstore.StorageEvent) (e *SucceededEven
 	}, nil
 }
 
-func NewSucceededCommand(source string, position float64) *eventstore.Command {
+func NewSucceededCommand(source string, position decimal.Decimal) *eventstore.Command {
 	return &eventstore.Command{
 		Action: eventstore.Action[any]{
 			Creator:  Creator,