feat: json5 source support

[tenuous-guidance]

Fixes #122

My biggest concern here is that it's easy to typo, but I'm not sure what a better naming might be? Maybe JsonFive but that would likely break user expectations.

[tenuous-guidance]

$ cargo update -p=toml_edit --precise=0.21.0
error: There are multiple `toml_edit` packages in your project, and the specification `toml_edit` is ambiguous.
Please re-run this command with one of the following specifications:
  [email protected]
  [email protected]

$ cargo tree -i toml_edit
toml_edit v0.21.1
└── toml v0.8.8
    ├── confik v0.11.7
    │   [dev-dependencies]
    │   └── confik-macros v0.11.1 (proc-macro)
    │       └── confik v0.11.7 (*)
    └── trybuild v1.0.99
        [dev-dependencies]
        └── confik-macros v0.11.1 (proc-macro) (*)
    [dev-dependencies]
    └── confik-macros v0.11.1 (proc-macro) (*)

$ cargo tree -i [email protected]
error: package ID specification `[email protected]` did not match any packages
Did you mean one of these?

  [email protected]

$ cargo update [email protected] --precise=0.21.0
    Updating crates.io index
error: failed to select a version for the requirement `toml_edit = "^0.22.20"`
candidate versions found which didn't match: 0.21.0
location searched: crates.io index
required by package `proc-macro-crate v3.2.0`
    ... which satisfies dependency `proc-macro-crate = "^3"` (locked to 3.2.0) of package `borsh-derive v1.5.1`
    ... which satisfies dependency `borsh-derive = "~1.5.1"` (locked to 1.5.1) of package `borsh v1.5.1`
    ... which satisfies dependency `borsh = "^1.1.1"` (locked to 1.5.1) of package `rust_decimal v1.36.0`
    ... which satisfies dependency `rust_decimal = "^1"` (locked to 1.36.0) of package `confik v0.11.7 (/home/user/git_repo/3pp/confik/confik)`
    ... which satisfies dependency `confik = "^0.11"` (locked to 0.11.7) of package `confik-macros v0.11.1 (/home/user/git_repo/3pp/confik/confik-macros)`

I think we're hitting a bug in cargo update. Running cargo update [email protected] --precise=0.21.0 will work, but only until we change toml_edit version.

How would you like to proceed @robjtede?