feat(python): add upper_bound and lower_bound methods to Series

[alexander-beedie]

Adds the missing methods via @expr_dispatch, along with some test coverage.

Example:

pl.Series( "s", dtype=pl.UInt16 ).upper_bound()

# shape: (1,)
# Series: 's' [u16]
# [
#     65535
# ]

pl.Series( "s", dtype=pl.Int16 ).lower_bound()

# shape: (1,)
# Series: 's' [i16]
# [
#     -32768
# ]

[ritchie46]

Nice! And the kryptonite? ;)

[alexander-beedie]

Nice! And the kryptonite? ;)

You would not believe the sound my facepalm just made; I think there was an echo...😅