Fixes these build errors I'm getting locally with `tcl-devel-9.0.0-7.fc42.x86_64`.
I guess Tcl 9 broke this.
```
passes/cmds/sdc/sdc.cc:438:6: error: no matching function for call to 'Tcl_ListObjLength'
438 | if (Tcl_ListObjLength(interp, listObj, &listLength) == TCL_OK) {
| ^~~~~~~~~~~~~~~~~
/usr/include/tclDecls.h:1788:13: note: candidate function not viable: no known conversion from 'int *' to 'Tcl_Size *' (aka 'long *') for 3rd argument
1788 | EXTERN int Tcl_ListObjLength(Tcl_Interp *interp,
| ^
1789 | Tcl_Obj *listPtr, Tcl_Size *lengthPtr);
| ~~~~~~~~~~~~~~~~~~~
passes/cmds/sdc/sdc.cc:446:8: error: no matching function for call to 'Tcl_ListObjLength'
446 | if (Tcl_ListObjLength(interp, subListObj, &subListLength) == TCL_OK) {
| ^~~~~~~~~~~~~~~~~
/usr/include/tclDecls.h:1788:13: note: candidate function not viable: no known conversion from 'int *' to 'Tcl_Size *' (aka 'long *') for 3rd argument
1788 | EXTERN int Tcl_ListObjLength(Tcl_Interp *interp,
| ^
1789 | Tcl_Obj *listPtr, Tcl_Size *lengthPtr);
| ~~~~~~~~~~~~~~~~~~~
```
From https://github.com/YosysHQ/yosys/pull/5497#issuecomment-3561398279, for ENABLE_ABC=1 to be valid, either ABC must be linked (LINK_ABC=1), or it must be possible to spawn executables (DISABLE_SPAWN=0). This configuration (ENABLE_ABC=1 LINK_ABC=0 DISABLE_SPAWN=1) already fails compilation in `abc.cc` trying to call `run_command()` which doesn't exist if DISABLE_SPAWN=1. All we are doing here is catching the known bad configuration and providing an explanation for why it isn't working.
- functions that have a const `[]` operator method now support `__getitem__` in Python
- fields of a pointer type now return a `reference_internal` instead of a `copy` because classes referenced to by pointers typically aren't copyable (e.g. RTLIL::Wire, RTLIL::Module, etc)
- removed duplicate of test_script.py
