TSM1 reader accessor struct: ensure 64bit alignment

[skladd]

• use pointers to allocated uin64 values instead field values
• fixes "panic: unaligned 64-bit atomic operation" with Golang v1.20

[skladd]

If compiling with go 1.20, influxd crashed after some time:

panic: unaligned 64-bit atomic operation

goroutine 23 [running]:
runtime/internal/atomic.panicUnaligned()
    /usr/lib/go-1.20/src/runtime/internal/atomic/unaligned.go:8 +0x24
runtime/internal/atomic.Xadd64(0x30bad54, 0x1)
    /usr/lib/go-1.20/src/runtime/internal/atomic/atomic_arm.s:258 +0x14
github.com/influxdata/influxdb/tsdb/engine/tsm1.(*accessor).incAccess(...)
    /go/github.com/simonvetter/influxdb/tsdb/engine/tsm1/reader.go:1497

This error didn't occur with golang 1.16.
Golang 1.19 brought own atomic.Uint64 types ensuring correct alignment, but this would break compiling using older go releases. Hence this fix via pointers.

Notes regarding alignment for atomic functions:
https://pkg.go.dev/sync/atomic#pkg-notes