fix(parallel): add maxsplit=1 to prevent ValueError on values containing '='

[devteamaegis]

What's broken

_parse_prefixed_args() in src/promptflow-parallel/promptflow/parallel/_config/parser.py crashes with ValueError: too many values to unpack (expected 2) whenever an argument value contains the = character. This affects base64-encoded values (which use = as padding), URLs with query strings, and any other value embedding =. For example, passing --pf_input_token=SGVsbG8gV29ybGQ= (base64 for "Hello World") raises the error immediately.

Why it happens

Line 88 calls arg.split("=") with no maxsplit, so a value like name=base64== splits into three elements and the two-variable unpack fails.

Fix

Changed arg.split("=") to arg.split("=", 1) so only the first = is used as the name/value delimiter. The rest of the string is preserved intact as the value.

Test

Added test_parse_prefixed_args_value_with_equals to tests/parallel/unittests/_config/test_parse.py. It passes a base64-padded token argument and asserts the full value (including trailing =) is parsed correctly without raising.

Fixes #4174

[github-actions]

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