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/event.go

@@ -5,6 +5,8 @@ import (
 	"reflect"
 	"time"
 
+	"github.com/shopspring/decimal"
+
 	"github.com/zitadel/zitadel/internal/zerrors"
 )
 
@@ -44,7 +46,7 @@ type Event interface {
 	// CreatedAt is the time the event was created at
 	CreatedAt() time.Time
 	// Position is the global position of the event
-	Position() float64
+	Position() decimal.Decimal
 
 	// Unmarshal parses the payload and stores the result
 	// in the value pointed to by ptr. If ptr is nil or not a pointer,