Migrate orderbook API from warp to axum

[jmg-duarte]

Description

This PR migrates the orderbook API from Warp to Axum. The migration modernizes our web framework while maintaining API
compatibility, with improved code organization and reduced complexity (~200 lines removed).

Changes

• Replace Warp filters with Axum Router and centralized AppState for dependency injection
• Migrate all 18 API endpoints (v1 and v2) to Axum handler functions
• Update dependencies: remove warp, add axum, tower, tower-http
• Reorganize routes hierarchically with .nest(), alphabetically by prefix
• Fix route conflicts using .merge() for multiple HTTP methods on same path
• Fix bug in get_trades_v2 (use database_read instead of database_write)
• Add comprehensive E2E test suite for HTTP behavior validation in malformed_requests.rs

Breaking Changes:

• JSON deserialization errors now return 422 instead of 400 (Axum convention)
• Deserialization error responses return plain text instead of JSON

How to test

Existing tests + staging

I deployed these changes to base staging to ensure metrics were working, here's the graph

Follow up:

Unmarked spots are running main, the wrong image was labeling endpoints with unknown because it was a fallback.
That code has been removed and replaced with the current metric labeling scheme.

That scheme can be improved (read, made less verbose and error prone while being more general) but we need to change the metrics label, which I didn't do to minimize changes.

[gemini-code-assist]

Code Review

This pull request migrates the orderbook API from Warp to Axum, modernizing the web framework and improving code organization. The changes include replacing Warp filters with Axum Router, migrating API endpoints, updating dependencies, and adding an E2E test suite. The review focuses on identifying critical and high severity issues, with actionable suggestions for improvement, while adhering to the repository's stricter code review style guide. One comment was modified to explicitly reference a relevant repository rule.

[MartinquaXD]

These handlers could also use database_read like their v1 counter parts.

[jmg-duarte]

8ebb11c

[MartinquaXD]

Could we reduce the usage of with_labelled_metrics? Given that axums paths just use a simple string to define them this should be easier than before even.
I think a structure similar to what we had before would be nicer to read. Not sure if this possible though since these handlers all have different types so some boxing or so would probably be needed. 🤔

let routes = [
    ("v1/solver_competition/latest", axum::routing::get(handler)
];

routes.into_iter().map(|(path, handler)|  {
    with_labelled_metric(path, handler)
})
.collect()

[jmg-duarte]

There's a small issue with your approach — not all routes match their label 😭

IMO we should make them match the label and in that case, we get better, we should be able to apply a middleware wholesale because we can get the path with placeholder

We might be able to simplify further with the TraceLayer and MatchedPath too
https://docs.rs/axum/latest/axum/extract/struct.MatchedPath.html

In summary: if the team is ok with the rename (I am!) we can make this whole thing even simpler

We can also move with this as is, and rename later so we are sure nothing broke

[extrawurst]

JSON deserialization errors now return 422 instead of 400 (Axum convention)

Is this in our API docs anywhere that we have to update aswell?