Implement Session Module

[Mkalbani]

Description

Create a session module that manages a single play session, tying together player, puzzle progress, timer, and score.

Acceptance Criteria

• A session module exists under src/session/mod.rs
• Session struct holds player ref, active puzzle, timer, and current score
• Session can be started, paused, and ended
• On end, session data is passed to persistence and leaderboard modules
• Unit tests cover session lifecycle and data handoff

[Emeka000]

I have experience with rust and can solve this issue in due time so can I work on this ?

[grantfox-oss]

🦊 GrantFox — @Emeka000 has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #19)
2. Your PR will be reviewed by the MindFlowInteractive maintainers

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