fix(sol): use pinned compiler for bb sol build (#24624)

## Summary
- Backport the Foundry config fix from
[#24620](#24620) to
`merge-train/spartan`.
- Move the `barretenberg/sol` `solc` setting into `[profile.default]` so
Foundry actually uses `../../l1-contracts/solc-0.8.30`.

## Why
[#24620](#24620)
fixed the v5 train after `bb-sol` ignored the intended pinned compiler
and fell back to Foundry's SVM download path. `merge-train/spartan` had
the same TOML scoping issue.

## Verification
- `forge config --json` in `barretenberg/sol` reports `"solc":
"../../l1-contracts/solc-0.8.30"`.
- `make bb-sol` passed.

---
*Created by
[claudebox](https://claudebox.work/v2/sessions/2b8c305bd7244e7e) ·
group: `slackbot`*

Author: AztecBot

barretenberg/sol/foundry.toml

@@ -9,14 +9,14 @@ gas_limit = 900000000000000000
 bytecode_hash = "none"
 evm_version = "cancun"
 
-[fuzz]
-runs = 2
-
 # Use the pre-downloaded solc binary from l1-contracts. l1-contracts' build is
 # the single owner of the svm download; pointing other forge projects at the
 # same binary avoids parallel svm downloads racing on ~/.svm.
 solc = "../../l1-contracts/solc-0.8.30"
 
+[fuzz]
+runs = 2
+
 [lint]
 ignore = ["./lib/**"]
 exclude_lints = [