feat(balance): Permit One-handed casting (#5919)

* One-handed casting

Allow one-handed weapons to impede, but not stop, casting.

* style(autofix.ci): automated formatting

* fix import type on flag.h

should we even be importing it? Idk

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

src/handle_action.cpp

@@ -1456,7 +1456,7 @@ static void cast_spell()
     spell &sp = *u.magic->get_spells()[spell_index];
 
     if( u.is_armed() && !sp.has_flag( spell_flag::NO_HANDS ) &&
-        !u.primary_weapon().has_flag( flag_MAGIC_FOCUS ) ) {
+        !u.primary_weapon().has_flag( flag_MAGIC_FOCUS ) && u.primary_weapon().is_two_handed( u ) ) {
         add_msg( game_message_params{ m_bad, gmf_bypass_cooldown },
                  _( "You need your hands free to cast this spell!" ) );
         return;

src/magic.cpp

@@ -25,6 +25,7 @@
 #include "enums.h"
 #include "event.h"
 #include "field.h"
+#include "flag.h"
 #include "game.h"
 #include "generic_factory.h"
 #include "input.h"
@@ -737,6 +738,10 @@ int spell::casting_time( const Character &guy ) const
                                           guy.encumb( body_part_arm_l ) + guy.encumb( body_part_arm_r ) - 20 );
         casting_time += arms_encumb * 2;
     }
+    if( guy.is_armed() && !has_flag( spell_flag::NO_HANDS ) &&
+        !guy.primary_weapon().has_flag( flag_MAGIC_FOCUS ) ) {
+        casting_time = std::round( casting_time * 1.5 );
+    }
     return casting_time;
 }