Update coverage for error and config packages

[leodziki]

Description

Currently, coverage rate has been upgraded to 80-100% in nativelink-error and nativelink-config packages.
Bazel test and cargo test both passed. And Pre-commit passed in direnv and everything is perfect.

Fixes #1401

Type of change

• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to
  not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Bazel test, cargo test and pre-commit

Checklist

• Tests added/amended
• bazel test //... passes locally

---

This change is 

[adam-singer]

Reviewed 5 of 6 files at r1, all commit messages.
Reviewable status: 0 of 2 LGTMs obtained, and 5 of 6 files reviewed, and 1 discussions need to be resolved

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nativelink-error/src/lib.rs line 154 at r1 (raw file):

impl From<prost::DecodeError> for Error {
    fn from(err: prost::DecodeError) -> Self {
        Error::new(Code::Internal, err.to_string())

Lets not change this since rest of the code follows this pattern for now.

[adam-singer]

@leodziki the commits would need to be squashed before we could land this

Reviewed 3 of 4 files at r2.
Reviewable status: 0 of 2 LGTMs obtained, and 6 of 7 files reviewed, and pending CI: Bazel Dev / macos-13, Bazel Dev / macos-14, Bazel Dev / ubuntu-24.04, Cargo Dev / macos-13, Cargo Dev / ubuntu-22.04, Coverage, Installation / macos-13, Installation / macos-14, Installation / ubuntu-22.04, NativeLink.com Cloud / Remote Cache / macos-14, NativeLink.com Cloud / Remote Cache / ubuntu-24.04, Publish image, Publish nativelink-worker-init, Publish nativelink-worker-lre-cc, Remote / large-ubuntu-22.04, Web Platform Deployment / macos-14, Web Platform Deployment / ubuntu-24.04, asan / ubuntu-22.04, docker-compose-compiles-nativelink (22.04), integration-tests (22.04), macos-13, ubuntu-20.04 / stable, ubuntu-22.04, ubuntu-22.04 / stable, windows-2022 / stable, and 1 discussions need to be resolved