fix: better package name validation and error messages for nargo new/init

[asterite]

Description

Problem

Resolves #8919
Resolves #4189

Summary

Also, since it was in the same codebase, now running nargo init on a directory that has a Nargo.toml file will not overwrite that file and give a proper error (like cargo init does).

The error messages are now similar to those used by cargo new/init, though I changed some minor things (they always surround chars and name with backticks, but I think it's more common to use single and double quotes respectively).

Some examples:

$ nargo new 'hello world'
Error: invalid character ' ' in package name "hello world", characters must be ASCII alphanumeric characters or '_' (underscore)
If you need a package name to not match the directory name, consider using the `--name` flag.

$ nargo new '1two'
Error: invalid character '1' in package name "1two", the name cannot start with a digit
If you need a package name to not match the directory name, consider using the `--name` flag.

$ nargo new '!hello'
Error: invalid character '!' in package name "!hello", the first character must be an ASCII alphabetic character or '_' (underscore)
If you need a package name to not match the directory name, consider using the `--name` flag.

$ nargo new 'test-noir'
Error: invalid character '-' in package name "test-noir", characters must be ASCII alphanumeric characters or '_' (underscore)
If you need a package name to not match the directory name, consider using the `--name` flag.

$ pwd
/Users/asterite/Sandbox/nargo_new/foo bar

$ nargo init
Error: invalid character ' ' in package name "foo bar", characters must be ASCII alphanumeric characters or '_' (underscore)
If you need a package name to not match the directory name, consider using the `--name` flag.

Additional Context

Documentation

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'Compilation Time'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.20.

Benchmark suite	Current: c535ba8	Previous: 8a7046b	Ratio
private-kernel-inner	2.774 s	2.304 s	1.20

This comment was automatically generated by workflow using github-action-benchmark.

CC: @TomAFrench

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'Execution Time'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.20.

Benchmark suite	Current: 19190ff	Previous: 2cfc786	Ratio
rollup-merge	0.004 s	0.003 s	1.33

This comment was automatically generated by workflow using github-action-benchmark.

CC: @TomAFrench

[aakoshh]

Looks good!

FWIW I agree with not allowing - in the name. It takes out some of the guesswork when adding dependencies.