Add docs for lease close reasons

[linear]

Document the lease close reason enum values defined in akash/market/v1/types.proto.

Source: https://github.com/akash-network/chain-sdk/blob/3ccaa4d6f9d1569fd68853954c6dc60a0d619207/proto/node/akash/market/v1/types.proto#L27

Each enum value should be documented with:

• What triggers the close reason
• Who can emit it (tenant vs provider vs chain)
• Expected downstream behavior (escrow settlement, bid/order state transitions, etc.)
• Any operational guidance for tenants/providers when they encounter the reason