Solution id is string (#3088)

# Description
This PR changes the type of the `id` column in the `proposed_solutions`
table from `i64` to `numeric(78,0)`. This adjustment prevents potential
overflow issues from `u64` values in the driver API, which could
previously lead to [failed u64 -> i64
conversions](https://github.com/cowprotocol/services/blob/main/crates/autopilot/src/infra/persistence/mod.rs#L154)
and errors when saving proposed solutions.

Alternative approaches considered:

1. Dropping the `id` column: While feasible, this would prevent reusing
the existing `domain::competition::Solution` object in the autopilot and
would require either creating a new domain object or generating IDs
dynamically when reading the solution from database, both of which are
not great ideas.
2. Changing the API type to `u32`: A more invasive change, requiring
modifications to the driver API and adjustments by solvers (e.g.,
Copium, which sometimes reports IDs exceeding `i64::MAX`).

After evaluating these options, I chose the least disruptive solution of
converting `id` to `numeric(78,0)`.

# Changes
<!-- List of detailed changes (how the change is accomplished) -->

- [ ] Change the type of "id" column, from BigInt to numeric(78,0)

## How to test
Existing tests.

<!--
## Related Issues

Fixes #
-->

crates/autopilot/src/infra/persistence/mod.rs

@@ -151,7 +151,7 @@ impl Persistence {
                 .map(|(uid, participant)| {
                     let solution = Solution {
                         uid: uid.try_into().context("uid overflow")?,
-                        id: i64::try_from(participant.solution().id()).context("block overflow")?,
+                        id: u256_to_big_decimal(&participant.solution().id().into()),
                         solver: ByteArray(participant.solution().solver().0 .0),
                         is_winner: participant.is_winner(),
                         score: u256_to_big_decimal(&participant.solution().score().get().0),

crates/database/src/solver_competition.rs

@@ -89,7 +89,7 @@ pub struct Solution {
     pub uid: i64,
     // Id as reported by the solver (solvers are unaware of how other solvers are numbering their
     // solutions)
-    pub id: i64,
+    pub id: BigDecimal,
     pub solver: Address,
     pub is_winner: bool,
     pub score: BigDecimal,
@@ -140,7 +140,7 @@ async fn save_solutions(
     builder.push_values(solutions.iter(), |mut b, solution| {
         b.push_bind(auction_id)
             .push_bind(solution.uid)
-            .push_bind(solution.id)
+            .push_bind(&solution.id)
             .push_bind(solution.solver)
             .push_bind(solution.is_winner)
             .push_bind(&solution.score)
@@ -244,7 +244,7 @@ pub async fn fetch(
     #[derive(sqlx::FromRow)]
     struct Row {
         uid: i64,
-        id: i64,
+        id: BigDecimal,
         solver: Address,
         is_winner: bool,
         score: BigDecimal,
@@ -410,21 +410,21 @@ mod tests {
         let solutions = vec![
             Solution {
                 uid: 0,
-                id: 0,
+                id: 0.into(),
                 solver: ByteArray([1u8; 20]), // from solver 1
                 orders: vec![Default::default()],
                 ..Default::default()
             },
             Solution {
                 uid: 1,
-                id: 0,
+                id: 0.into(),
                 solver: ByteArray([2u8; 20]), // from solver 2
                 orders: vec![Default::default()],
                 ..Default::default()
             },
             Solution {
                 uid: 2,
-                id: 1,
+                id: 1.into(),
                 solver: ByteArray([2u8; 20]), // from solver 2
                 orders: vec![
                     Order {

database/README.md

@@ -352,7 +352,7 @@ All solutions reported by solvers, that were part of a solver competition. A sol
 ---------------|-----------|----------|--------
  auction\_id   | bigint    | not null | auction for which the solution was proposed 
  uid           | bigint    | not null | unique id of the proposed solution within a single auction
- id            | bytea     | not null | id of the proposed solution as reported by the solver
+ id            | numeric   | not null | id of the proposed solution as reported by the solver
  solver        | bytea     | not null | solver submission address
  is\_winner    | boolean   | not null | specifies if a solver that proposed this solution is required to execute the solution
  score         | numeric   | not null | score of a solution, based on a scoring criteria used at the time of competition

database/sql/V074__drop_solution_id.sql

@@ -0,0 +1,3 @@
+-- Change the type of "id" column in proposed_solutions table from bigint to text
+ALTER TABLE proposed_solutions
+ALTER COLUMN id TYPE numeric(78,0) USING id::numeric(78,0);