after investigation into wp rewrite rules for author and with help of @Mark Davidson everything is now working perfect author archives pagination and feed rss atom etc.
below is the code which i have created and pasted here to help others, Thanks Mark Davidson for providing a pattern.
// add our custom rewrite rules for author archives
add_action('author_rewrite_rules', 'my_author_rewrite_rules');
function my_author_rewrite_rules() {
$author_rules['author/([0-9]+)/?$'] = 'index.php?author=$matches[1]';
$author_rules['author/([0-9]+)/page/?([0-9]{1,})/?$'] = 'index.php?author=$matches[1]&paged=$matches[2]';
$author_rules['author/([0-9]+)/(feed|rdf|rss|rss2|atom)/?$'] = 'index.php?author=$matches[1]&feed=$matches[2]';
$author_rules['author/([0-9]+)/feed/(feed|rdf|rss|rss2|atom)/?$'] = 'index.php?author=$matches[1]&feed=$matches[2]';
return $author_rules;
}
this function will totally replace the author rewrite rules, if anyone want to add new rules and don't want to replace existing then he/she need to supply $author_rules argument in function like.
function my_author_rewrite_rules($author_rules) {
// new rules here
}