broadcast_binary_elementwise silently truncates rhs to lhs length

[MarcoGorelli]

Checks

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

pl.Series(['1', '43242', '121']).str.zfill(pl.Series([2, 3]))

Log output

shape: (2,)
Series: '' [str]
[
        "01"
        "43242"
]

Issue description

The last element of the right-hand-size was silently discarded

Expected behavior

I think it should raise a ShapeError

Installed versions

--------Version info---------
Polars:               0.20.23
Index type:           UInt32
Platform:             Linux-5.15.146.1-microsoft-standard-WSL2-x86_64-with-glibc2.35
Python:               3.11.9 (main, Apr  6 2024, 17:59:24) [GCC 11.4.0]

----Optional dependencies----
adbc_driver_manager:  <not installed>
cloudpickle:          3.0.0
connectorx:           <not installed>
deltalake:            <not installed>
fastexcel:            <not installed>
fsspec:               2024.3.1
gevent:               <not installed>
hvplot:               0.9.2
matplotlib:           3.8.4
nest_asyncio:         1.6.0
numpy:                1.26.4
openpyxl:             <not installed>
pandas:               2.2.2
pyarrow:              15.0.2
pydantic:             <not installed>
pyiceberg:            <not installed>
pyxlsb:               <not installed>
sqlalchemy:           <not installed>
xlsx2csv:             <not installed>
xlsxwriter:           <not installed>

[ritchie46]

This should be handled by zfill before going into broadcast I would say. zip also truncates.

Now, I agree this is error prone, so maybe we should add a shape assert to ensure we don't misuse it.