WIP: Add Playfair cracker

[RotationMatrix]

Companion to my PR in Ciphey.

[todo]

Ciphertext is not playfair if is contains a repeated digraph (AA, BB, CC, etc.)

CipheyCore/src/ciphers/playfair.cpp

Lines 16 to 21 in ca59031

	// TODO: Ciphertext is not playfair if is contains a repeated digraph (AA, BB, CC, etc.)
	// TODO: Ciphertext is not playfair if is contains more than 25 distinct letters.
	// if (observed.size() > 25) {
	// return 0.;
	// }

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This comment was generated by todo based on a TODO comment in ca59031 in #13. cc @RotationMatrix.

[todo]

Ciphertext is not playfair if is contains more than 25 distinct letters.

CipheyCore/src/ciphers/playfair.cpp

Lines 18 to 23 in ca59031

	// TODO: Ciphertext is not playfair if is contains more than 25 distinct letters.
	// if (observed.size() > 25) {
	// return 0.;
	// }
	// For now, we can ignore ciphertext with non-Latin characters.

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This comment was generated by todo based on a TODO comment in ca59031 in #13. cc @RotationMatrix.

[todo]

Use ciphertext to guess the 26th letter.

CipheyCore/src/ciphers/playfair.cpp

Lines 36 to 41 in ca59031

	// TODO: Use ciphertext to guess the 26th letter.
	std::vector<char_t> alphabet {
	'a', 'b', 'c', 'd', 'e',
	'f', 'g', 'h', 'i', 'k',
	'l', 'm', 'n', 'o', 'p',
	'q', 'r', 's', 't', 'u',

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This comment was generated by todo based on a TODO comment in ca59031 in #13. cc @RotationMatrix.