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/readmodel/last_successful_mirror.go

@@ -1,6 +1,8 @@
 package readmodel
 
 import (
+	"github.com/shopspring/decimal"
+
 	"github.com/zitadel/zitadel/internal/v2/eventstore"
 	"github.com/zitadel/zitadel/internal/v2/system"
 	"github.com/zitadel/zitadel/internal/v2/system/mirror"
@@ -8,7 +10,7 @@ import (
 
 type LastSuccessfulMirror struct {
 	ID       string
-	Position float64
+	Position decimal.Decimal
 	source   string
 }
 
@@ -53,7 +55,7 @@ func (h *LastSuccessfulMirror) Reduce(events ...*eventstore.StorageEvent) (err e
 
 func (h *LastSuccessfulMirror) reduceSucceeded(event *eventstore.StorageEvent) error {
 	// if position is set we skip all older events
-	if h.Position > 0 {
+	if h.Position.GreaterThan(decimal.NewFromInt(0)) {
 		return nil
 
 	}