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/v3/event.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"time"
 
+	"github.com/shopspring/decimal"
 	"github.com/zitadel/logging"
 
 	"github.com/zitadel/zitadel/internal/eventstore"
@@ -21,7 +22,7 @@ type event struct {
 	typ       eventstore.EventType
 	createdAt time.Time
 	sequence  uint64
-	position  float64
+	position  decimal.Decimal
 	payload   Payload
 }
 
@@ -84,8 +85,8 @@ func (e *event) Sequence() uint64 {
 	return e.sequence
 }
 
-// Sequence implements [eventstore.Event]
-func (e *event) Position() float64 {
+// Position implements [eventstore.Event]
+func (e *event) Position() decimal.Decimal {
 	return e.position
 }