feat(rocksdb): remove getters for internal rocksdb handles, expose backup instead

[rymnc]

• Revert "chore(rocksdb): getter for inner database handle (chore(rocksdb): getter for inner database handle #2532)"
• fix(rocksdb): expose backup and restore functionality instead of inner dbs

Linked Issues/PRs

• chore(rocksdb): getter for inner database handle #2532 (comment)

Description

• creates a feature backup and 2 functions, backup and restore.
• not too many config options available at the moment
• bubbled it to CombinedDatabase, similarly to the prune api from rocksdb.

Checklist

• Breaking changes are clearly marked as such in the PR description and changelog
• New behavior is reflected in tests
• The specification matches the implemented behavior (link update PR if changes are needed)

Before requesting review

• I have reviewed the code myself
• I have created follow-up issues caused by this PR and linked them here

After merging, notify other teams

[Add or remove entries as needed]

• Rust SDK
• Sway compiler
• Platform documentation (for out-of-organization contributors, the person merging the PR will do this)
• Someone else?

Copilot reviewed 5 out of 8 changed files in this pull request and generated no comments.

Files not reviewed (3)

• crates/fuel-core/src/state/rocks_db.rs: Evaluated as low risk
• CHANGELOG.md: Evaluated as low risk
• crates/fuel-core/src/state/historical_rocksdb.rs: Evaluated as low risk

Comments suppressed due to low confidence (4)

crates/fuel-core/src/combined_database.rs:89

• The error message could be more descriptive. Consider including more context about the failure.

crate::database::Error::BackupError(anyhow::anyhow!("Failed to create temporary backup directory: {}", e))

crates/fuel-core/src/combined_database.rs:163

• The error message could be more descriptive. Consider including more context about the failure.

crate::database::Error::RestoreError(anyhow::anyhow!("Failed to create temporary restore directory: {}", e))

crates/fuel-core/src/combined_database.rs:133

• Ensure that temporary directories are properly removed in case of errors to avoid leaving residue.

std::fs::remove_dir_all(temp_backup_dir.path()).map_err(|e| {

crates/fuel-core/src/combined_database.rs:207

• Ensure that temporary directories are properly removed in case of errors to avoid leaving residue.

std::fs::remove_dir_all(temp_restore_dir.path()).map_err(|e| {