fix(deps): bump tokio-postgres to 0.7.18

[tobyhede]

Summary

Bumps tokio-postgres in Cargo.lock from 0.7.13 → 0.7.18 to address GHSA-3gjw-f78c-vvpw (Medium; affected >= 0.4.0, < 0.7.18). Resolves Dependabot alert #55.

Lockfile-only change; no Cargo.toml edits (all manifests already use tokio-postgres = "0.7").

Lockfile changes

• tokio-postgres 0.7.13 → 0.7.18
• Companion/transitive bumps pulled in by the resolver: postgres-types 0.2.9 → 0.2.14, postgres-derive 0.4.6 → 0.4.9, whoami 1.6.0 → 2.1.3, wasite 0.1.0 → 1.0.2, phf/phf_shared 0.11.3 → 0.13.1, serde_json 1.0.140 → 1.0.151; added objc2-core-foundation, objc2-system-configuration, zmij
• libredox 0.1.3 → 0.1.24 (required: whoami 2.x needs a newer libredox than was locked)
• postgres-protocol (0.6.12) and tokio-postgres-rustls (0.13.0) unchanged

Verification

• cargo tree -i tokio-postgres --workspace: single version, tokio-postgres v0.7.18
• cargo check --workspace --all-targets: passes

[freshtonic]

I think this entry describes a regression that no user saw. The tokio-postgres bump and the ErrorChain fix are both in this PR, so a released Proxy never logged a bare db error. 3.0.1 logs db error: ERROR: … and so does this branch. A reader of the release notes would think that database errors in the logs were broken in a released version.

I suggest that you remove this entry, or merge one sentence into the ### Security entry below. For example: "Logged database errors still include the message from PostgreSQL." Not blocking.

[freshtonic]

Approving. The dependency bump is correct and the follow-up work is sound.

What I checked

• ErrorChain gives the same log text as before the bump. Under 0.7.13, Display rendered db error: ERROR: <msg>. Now ErrorChain renders the kind (db error), then : , then the DbError source (ERROR: <msg>). ConfigError::Database and Error::Config are #[error(transparent)], so both Display and source() forward to the inner error and the chain stays correct through the crate wrappers.
• No client-facing path sends a tokio_postgres::Error to the client. The only tokio-postgres clients are the schema loader, the EQL version probe and the migrate CLI. Their errors are logged, not converted in error_to_response, so no client can get a bare db error in an ErrorResponse.
• The remaining err.to_string() log sites (ConnectionTimeout, prometheus, TLS, config reload) cannot contain a tokio_postgres::Error, so it is correct to leave them unchanged.
• assert_db_error compares severity() and message() on the DbError. This is more precise than the old string compare, and the passthrough test no longer needs its own nested match.
• All required checks pass on 9eaa4bc.

Non-blocking

1. The PR description is out of date. It says "Lockfile-only change; no Cargo.toml edits", but the branch now also adds ErrorChain, changes nine log sites, adds two test helpers and adds CHANGELOG entries. Please update the summary so the squash commit and the release notes match the change.
2. See the inline comment on the ### Fixed CHANGELOG entry.
3. Small point: ErrorChain skips a cause when the text rendered so far ends with that cause. A short cause (for example timeout) can match the end of an unrelated message and get dropped. This is acceptable for log output. If you want it exact, compare only against the parent's own Display, not the accumulated string. No change is necessary.