Upgrade cargo dependencies: `buf_redux`, `multipart`, `nom`

[josecelano]

cargo check output:

warning: the following packages contain code that will be rejected by a future version of Rust: buf_redux v0.8.4, multipart v0.18.0, nom v5.1.2
note: to see what the problems were, use the option `--future-incompat-report`, or run `cargo report future-incompatibilities --id 14`

[josecelano]

And also, review unused dependencies:

$ cargo +nightly udeps --all-targets
unused dependencies:
`torrust-tracker v2.3.0 (/home/josecelano/Documents/github/committer/me/torrust/torrust-tracker)`
└─── dependencies
     └─── "hex"
`torrust-tracker-configuration v2.3.0 (/home/josecelano/Documents/github/committer/me/torrust/torrust-tracker/packages/configuration)`
└─── dependencies
     └─── "uuid"
`torrust-tracker-located-error v2.3.0 (/home/josecelano/Documents/github/committer/me/torrust/torrust-tracker/packages/located-error)`
└─── dependencies
     └─── "thiserror"
`torrust-tracker-test-helpers v2.3.0 (/home/josecelano/Documents/github/committer/me/torrust/torrust-tracker/packages/test-helpers)`
└─── dependencies
     └─── "tokio"
Note: They might be false-positive.
      For example, `cargo-udeps` cannot detect usage of crates that are only used in doc-tests.
      To ignore some dependencies, write `package.metadata.cargo-udeps.ignore` in Cargo.toml.

[josecelano]

• Update cargo dep r2d2_mysql from 21 to 23 #232
• Refactor: remove cargo dep warp and add hyper #233

[josecelano]

I've removed the warp dependency because we only used hyper through the warp package. It seems those packages were warp dependencies. So we do not have that message anymore.

cargo check output is clean now:

$ cargo check
    Finished dev [optimized + debuginfo] target(s) in 0.10s