Trigger the buffs gear grants on attack and defence - #3171

Fixes #3169

BCard type 95 subtypes 21/31/41/51 (a chance, on a landed hit, to put a card on the opponent or on oneself) were ignored. A new OnHitBuffService reads the attacker's and defender's gear and active buffs after every landed hit and rolls each line through IBuffService.InflictCardsAsync, so debuff resistance and immunity apply as for skill cards:

• attacker 21: card on the defender; attacker 31: card on the attacker
• defender 41: card on the attacker; defender 51: card on the defender

Nothing is put on a defender the hit killed. The "negated" subtypes (22/32/42/52) are left out: no item uses them in a way the data explains.

Client check

Tester (level 80) wears hat costume 8900 (8% card 4426 on self, 3% card 4424 on the enemy) and auto-attacks a Baby Dander for 60 s on Chicken Farm Path.

The card 4426 crescent icon shows on Tester's buff bar and above the character while it lasts.

Tests

• OnHitBuffTests: each of the four subtypes reaches InflictCardsAsync with the right target, caster, chance and card; a killed defender gets nothing.
• dotnet test on GameObject.Tests: 2030 passed.

Manual test plan

Added "Buffs triggered by hits" to documentation/manual-test-plan.md:

• Wear hat 8900 and auto-attack a monster for a minute: card 4426 shows on your buff bar now and then, and card 4424 lands on the monster.
• Gear that triggers on defence puts its card on you, or on the attacker, when you are hit (not checked in the client).

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