Sanma support

[Nihisil]

Below is approximate plan of what we need to do, full research required for full requirements.

Add full sanma support to the library:

• Add support for shanten calculations
• Add support for is_agari calculations
• Add support for hand yaku calculations
• Add support for scores calculations

[Apricot-S]

1. Tsumo Loss (ツモ損) handling

Using the four-player scoring logic as-is will cause underpayment on tsumo wins because Sanma has one fewer child compared to four-player mahjong.

Many Sanma rulesets (including common offline rules) split the missing North seat payment between the remaining two players.

Meanwhile, in Tenhou and Mahjong Soul ranked matches, "tsumo loss ON" is the default behavior, but tournament modes in both platforms allow switching this option ON/OFF.

We should decide whether the library will:

• support both modes (tsumo-loss ON/OFF), or
• choose one as the default behavior.

This affects the score calculation API and configuration.

2. Treatment of Nuki-dora (抜きドラ)

Sanma rules often include nuki-dora, but implementations differ:

The library already defines Meld.NUKI, but it has not been used internally so far.
We need to decide whether nuki-dora is:

• counted as a separate yaku (Mahjong Soul style), or
• merged into normal dora count (Tenhou style).

This affects yaku evaluation, scoring, and meld representation.

3. Handling of 2m–8m tiles

Standard Sanma excludes 2m–8m entirely.
We need to define behavior when a hand or meld containing these tiles is passed to the API:

• Should Sanma mode enable strict validation and reject such hands?
• Or should the library silently ignore/normalize them?
• Or should the core remain permissive and validation be optional?

This affects shanten, agari, and yaku evaluation.

4. Handling of Meld.CHI

Chi is normally disabled in Sanma.
If a user passes melds containing Meld.CHI while Sanma mode is active, we need to define:

• Should this be treated as invalid input?
• Should the library ignore chi melds?
• Or should chi be allowed only if the ruleset explicitly enables it?

This affects meld validation and agari logic.