Validate max size of import blob.

Import blob appears to only handle sensitive data with a max of 128 bytes. See this test:

```go
package client_test

import (
"fmt"
"io"
"strings"
"testing"

"github.com/google/go-cmp/cmp"
tpmclient "github.com/google/go-tpm-tools/client"
tpmserver "github.com/google/go-tpm-tools/server"
"github.com/google/go-tpm-tools/simulator"
)

func TestImportE2E(t *testing.T) {
sim, err := simulator.Get()
if err != nil {
t.Fatal(err)
}
defer sim.Close()

for i := 0; i < 256; i++ {
t.Run(fmt.Sprint(i), func(t *testing.T) {
testImport(t, sim, i)
})
}

}

func testImport(t *testing.T, tpmDev io.ReadWriteCloser, size int) {
ek, err := tpmclient.EndorsementKeyRSA(tpmDev)
if err != nil {
t.Fatal(err)
}
defer ek.Close()

secret := strings.Repeat("s", size)
blob, err := tpmserver.CreateImportBlob(ek.PublicKey(), []byte(secret), nil)
if err != nil {
t.Fatal(err)
}

out, err := ek.Import(blob)
if err != nil {
t.Fatalf("Import failed: size=%v, err=%v", size, err)
}
if diff := cmp.Diff(string(out), secret); diff != "" {
t.Errorf("unexpected output (-got +want): %s", diff)
}
}
```

At message size of 129 bytes and beyond, this test starts failing with:
```
Import failed: size=129, err=import failed: parameter 3, error code 0x15 : structure is the wrong size
```

Is that by the TPM spec or is there a something wrong with the encoding?

Start with the provided TestImportE2E reproduction, then trace CreateImportBlob and ek.Import to inspect how the sensitive data size is encoded and passed to the TPM. Compare the behavior at 128 and 129 bytes with the TPM specification. Done means establishing whether the limit is specified or an encoding defect, then adding regression coverage and fixing or documenting the result.

Written by the indexing model from the issue text.