Learn English – What does “of late he had fallen on evil days” mean in this sentence

The construction BE to VERB means, depending on context, BE expected/supposed/required to VERB. VERB may be any infinitive: simple, passive, perfect, or progressive (or any combination of these).

You are to leave immediately. = You are required to leave.
The prisoners were to be executed at dawn. = The prisoners were supposed to be executed at dawn.
She was to have been in New York on Thursday. = She was expected to have been there.
I am to be travelling all day tomorrow. = I am expected to be travelling—i.e. I expect to be travelling.

Negatives are a little tricky to paraphrase, because idiomatic use is unsymmetrical:

The prisoners were not to be executed until dawn. = They were not supposed to be executed. BUT
You are not to leave. = You are required not to leave, i.e. You are forbidden to leave.

And the negative passive has an additional possible meaning: BE not to be VERBen can mean BE impossible to VERB. So You are not to be distracted may be understood as either

1. You are required not be distracted, i.e., It is forbidden that you be distracted, OR
2. You are impossible to distract.

In this case it is clearly the latter which is meant: "I see I cannot distract you."

As an adjective, prize means “likely to win a prize”. This means that if the boar entered a contest, it would have a good chance of winning. It doesn't necessarily imply that the animal has ever entered a contest or ever will, just that it has the qualities that would make it a likely winner. This is mostly applied to animals (prize cow) and to plants (prize orchid), but can also be applied to other concepts (prize essay, prize performance, …).

Prize-winning would mean that the animal has won at least one prize.

Prized is rather different. A prized possession is something whose owner puts a high price on, i.e. something that the owner considers to be so valuable that he does not wish to part from it. It can either be objectively valuable, in the sense that it would fetch a high price if the owner sold it, or subjectively, in the sense that the owner does not want to part from it, perhaps for sentimental reasons. In the subjective sense, treasured is more often used than prized.