Split cardano-wallet-unit test suite into smaller packages

[paolino]

Problem

The cardano-wallet-unit test suite is too large, making it difficult to:

• Identify memory-hungry tests
• Debug OOM issues in CI
• Run focused test subsets efficiently

Currently we work around this by splitting tests at CI level using --match and --skip hspec flags, running 10 parallel jobs by module prefix:

• Byron + CLI
• DB.Sqlite + Pool
• Address
• Api
• Balance
• DB
• Primitive
• Shelley
• Other Wallet modules
• Control + Data utilities

Proposal

Split cardano-wallet-unit into multiple cabal test suites, e.g.:

• cardano-wallet-unit:cli
• cardano-wallet-unit:db
• cardano-wallet-unit:api
• cardano-wallet-unit:primitive
• etc.

This would:

• Make CI configuration cleaner (no --match/--skip flags)
• Allow independent dependency tracking per test group
• Enable easier local debugging of specific test areas
• Provide clearer test organization

Context

See PR #5082 for the CI workaround using hspec match patterns.