fix: missing pkg dependency of @sa11y/common

[mohanraj-r]

@sa11y/common is listed as a dev dependency of @sa11y/format because initially only common types declared in that pkg were being used in Typescript.
But currently non-type declarations from the common pkg are being used (e.g. errMsgHeader). This results in error when trying to install @sa11y/format on its own.

The pkg dependency checker in place has failed to catch this.

• Fix the missing dependency
• Install all @sa11y pkgs in isolation and fix any dependency issues
• Automate this check as much as possible