Support for ETBLOCK

### 🔍 Before submitting the issue

- [X] I have searched among the existing issues
- [X] I am using a Python virtual environment

### 🐞 Description of the bug

As described here, https://discuss.ansys.com/discussion/2365/unable-to-read-cdb-file-in-pyprimemesh, Ansys 2023 added ETBLOCK, and is using it in favour of ET

### 📝 Steps to reproduce

Cannot read cdb file generated by Ansys APDL 2023

### 💻 Which operating system are you using?

Linux

### 📀 Which ANSYS version are you using?

R2023

### 🐍 Which Python version are you using?

3.7

### 📦 Installed packages

```shell
NA
```

No source file or test is named in the issue. Start by reproducing the failure with a CDB file generated by Ansys APDL R2023 on Linux using Python 3.7, then locate the reader path that parses ET and determine where ETBLOCK is rejected. Done means the R2023 file can be read successfully and the relevant parsing behavior is covered by a test.

Written by the indexing model from the issue text.