Underscore: `_` variable in REPL #7327

Job	Run time
Test PIP Installable Packages	3m 27s
Check Debug build	3m 31s
Build LPython to WASM	5m 44s
Build Jupyter Kernel	3m 21s
LPython CI (3.10, ubuntu-latest)	7m 13s
Test CPython Interop (@pythoncall)	3m 34s
Run Integration tests with Python 3.9	3m 43s
LPython CI (3.10, macos-latest)	5m 4s
Run Integration tests with Python 3.10	3m 48s
Check Release build	5m 47s
LPython CI (3.10, windows-2019)	13m 30s
Run SymPy tests	4m 36s
Run Integration tests with Python 3.11	3m 53s
Run Integration tests with Python 3.12	3m 45s
Upload Tarball	34s
	1h 11m 30s

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