feat(validator-debt): better summarized debt

[bgm-malbeclabs]

Summary of Changes

This PR adds in more details for when debt collection is posted to slack and also summarizes debt collection for all epochs. It moves some of the debt-related slack composition to the validator-debt crate so we can reuse the existing structs instead of a many-arity function. It also adds total debt, total paid, and insufficient payment counts to the pay debt GenServer which are then posted to slack at the end of a debt collection run.

Closes malbeclabs/doublezero#2256.

Testing Verification

• This was tested locally in a private slack channel:

[Copilot]

Pull request overview

This PR enhances debt collection reporting by adding detailed summaries for both individual epochs and aggregated totals across all epochs. The changes move Slack notification logic into the validator-debt crate to improve code reusability and add tracking of total debt, total paid amounts, and insufficient payment counts throughout the debt collection process.

Key Changes:

• Refactored debt collection results to use detailed structs instead of simple counts
• Added cumulative tracking of debt metrics across epochs in the PayDebt GenServer
• Created a new endpoint to post aggregated debt summaries to Slack

Reviewed changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
scheduler/native/scheduler_doublezero/src/lib.rs	Added debt collection structs, new post_debt_summary NIF function, and modified pay_debt to return detailed collection results
scheduler/native/scheduler_doublezero/Cargo.toml	Added reqwest dependency for HTTP requests
scheduler/mix.exs	Removed trailing comma from deps() call
scheduler/lib/scheduler/worker/pay_debt.ex	Enhanced GenServer state to track cumulative debt metrics and post summary on completion
scheduler/lib/scheduler/validator_debt/debt_collection.ex	Created Elixir structs for debt collection results
scheduler/lib/scheduler/scheduler_doublezero.ex	Added NIF declaration for post_debt_summary
scheduler/CHANGELOG.md	Added changelog entry for debt summarization feature
crates/validator-debt/src/worker.rs	Moved post_debt_collection_to_slack function from slack-notifier with enhanced details
crates/validator-debt/src/transaction.rs	Changed debt collection results from counts to vectors of detailed results
crates/solana-cli/src/command/revenue_distribution/relay/mod.rs	Updated to use refactored debt collection posting function
crates/slack-notifier/src/validator_debt.rs	Removed post_debt_collection_to_slack function and changed post_to_slack visibility to public

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