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/repository/event.go

@@ -5,6 +5,8 @@ import (
 	"encoding/json"
 	"time"
 
+	"github.com/shopspring/decimal"
+
 	"github.com/zitadel/zitadel/internal/eventstore"
 )
 
@@ -18,7 +20,7 @@ type Event struct {
 	// Seq is the sequence of the event
 	Seq uint64
 	// Pos is the global sequence of the event multiple events can have the same sequence
-	Pos float64
+	Pos decimal.Decimal
 
 	//CreationDate is the time the event is created
 	// it's used for human readability.
@@ -91,7 +93,7 @@ func (e *Event) Sequence() uint64 {
 }
 
 // Position implements [eventstore.Event]
-func (e *Event) Position() float64 {
+func (e *Event) Position() decimal.Decimal {
 	return e.Pos
 }