feat: use correct mongodb client lifecycle

[RafaelCenzano]

Description

• Use proper mongodb client lifecycle and FastAPI dependency injection.
• Add MongoDB indexes to improve queries

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

[Copilot]

Pull request overview

This PR updates the backend’s MongoDB integration to use a proper application-scoped client lifecycle via FastAPI’s lifespan and propagates DB access through the request/app state, while also adding index creation for query performance.

Changes:

• Introduces MongoDB startup/shutdown hooks and stores Mongo client/database in app.state.
• Refactors route + database layers to pass Request so DB functions can access request.app.state.mongo_database.
• Adds MongoDB index creation (notably for LAF, and a setup function for Backtest).

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
server/app.py	Adds MongoDB/Valkey lifecycle management in lifespan.
server/database/mongo.py	New MongoDB setup/shutdown + get_database() helper using app.state.
server/database/valkey.py	Replaces print with structured logging and adds shutdown hook.
server/helpers/cache.py	Adds aiocache key builder that excludes Request from cache keys.
server/database/laf.py	Moves DB access to request.app.state, adds multiple indexes, updates cached helpers to accept Request.
server/routes/laf.py	Threads Request through LAF route handlers into DB functions.
server/database/loanertech.py	Moves DB access to request.app.state and updates function signatures accordingly.
server/routes/loanertech.py	Threads Request through LoanerTech route handlers into DB functions.
server/database/backtest.py	Moves DB access to request.app.state, adds caching key builder usage, introduces backtest_db_setup() for indexes.
server/routes/backtest.py	Threads Request through Backtest route handlers into DB functions.
server/database/init.py	Removes global Mongo client/database initialization.

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