Implement bitboard quiet-move generation

[binarylab2022-del]

Objective

Implement non-capturing move generation using the bitboard position
representation.

The bitboard implementation must produce the same quiet moves as the current
readable reference engine.

This issue covers:

• ordinary-piece quiet moves;
• flying-Dama quiet moves;
• promotion information;
• board-edge and blocker handling;
• equivalence validation.

Dependencies

This issue depends on:

• Issue Implement bitboard square mapping and position representation #4 — bitboard square mapping and position representation;
• Issue Build move-set comparison and perft validation tools #5 — canonical move and move-set comparison tools.

Implementation should begin after the interfaces introduced by Issues #4 and
#5 are stable.

Required work

1. Ordinary-piece quiet moves

For every ordinary piece:

• generate forward-left moves;
• generate forward-right moves;
• use the correct direction for each player;
• reject destinations outside the board;
• reject non-playable destinations;
• reject occupied destinations;
• prevent board-edge wraparound;
• record promotion when the destination reaches the promotion row.

Appropriate edge masks or precomputed destination tables should be used.

2. Flying-Dama quiet moves

For each Dama and each diagonal direction:

• follow the diagonal ray;
• add every empty destination;
• stop at the board edge;
• stop at the first occupied square;
• do not pass through friendly pieces;
• do not pass through opposing pieces.

A Dama may have several quiet destinations on the same open diagonal.

Precomputed diagonal-ray tables may be used.

3. Separate raw quiet moves from complete legal moves

The bitboard quiet generator should generate non-capturing moves only.

It must not claim to be a complete legal-move generator because capture
generation is outside this issue.

The architecture should clearly distinguish:

Raw bitboard quiet moves
        versus
Complete legal moves after mandatory-capture rules