fix(PythonCodeTableWriter): emit float("-inf") for negative infinity

[gaoflow]

Problem

PythonCodeTableWriter renders float("-inf") (negative infinity) as
float("inf") — valid Python syntax but the wrong value, silently
producing positive infinity when the generated code is executed.

import math, pytablewriter

writer = pytablewriter.PythonCodeTableWriter()
writer.table_name = "data"
writer.headers = ["val"]
writer.value_matrix = [[-math.inf], [math.inf]]
print(writer.dumps())

Before this fix:

data = [
    ["val"],
    [float("inf")],   # ← should be float("-inf")
    [float("inf")],
]

Root cause

dataproperty normalises every infinity value to Decimal('Infinity')
before type_value_map is applied, losing the sign. Both math.inf
and -math.inf therefore hit the same map entry
{Typecode.INFINITY: 'float("inf")'}.

Fix

Override _to_row_item in PythonCodeTableWriter to check the
original value in value_matrix when the mapped literal is
float("inf"). If the original was a negative-infinity float,
substitute float("-inf") instead.

After this fix

data = [
    ["val"],
    [float("-inf")],  # ✓ correct
    [float("inf")],   # ✓ correct
]

Tests

Added a parametrised test case covering -inf, +inf, and nan to
test/writer/text/sourcecode/test_python_code_writer.py.

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This pull request was prepared with the assistance of AI, under my direction and review.