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/handler/v2/statement.go

@@ -9,6 +9,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/shopspring/decimal"
 	"github.com/zitadel/logging"
 	"golang.org/x/exp/constraints"
 
@@ -83,7 +84,7 @@ type Statement struct {
 	AggregateType eventstore.AggregateType
 	AggregateID   string
 	Sequence      uint64
-	Position      float64
+	Position      decimal.Decimal
 	CreationDate  time.Time
 	InstanceID    string