gh-141571: argparse: avoid redundant early _set_color() call in HelpFormatter.__…

[chillakalyan]

Fixes: #141571

argparse currently initializes color twice when constructing a
HelpFormatter:

1. HelpFormatter.init() calls _set_color(color) immediately,
   using the default value color=True.
2. Later, argparse._get_formatter() instantiates a new formatter and
   calls formatter._set_color(self.color) again.

The first initialization is redundant and causes duplicate environment
lookups and repeated calls to colorize.can_colorize(), especially when
color=False. The actual color configuration only needs to happen once,
and the correct location is inside _get_formatter(), where formatter
instances are created.

This patch removes the early invocation of _set_color() in
HelpFormatter.init and simply stores the requested color preference:

self._color = color

The color initialization continues to happen once in
_get_formatter():

formatter._set_color(self.color)

This preserves the existing behavior for all consumers while avoiding
unnecessary work during HelpFormatter construction.