feat: #ensure_valid_syntax on tax ids (#1)

### Why?

As a user of TaxIds I want to make as few government database lookups as
possible. By making sure that the TaxId initializer only creates
instances that adhere to the specific TaxId type syntaxes we can avoid
any unnecessary lookups.

### What changed?

- Added the `tax_country_code` field to the TaxId struct. This field is
populated with the two-letter code at the start of the tax id value. IE:
`"SE"` in `"SE123456789101"`. This was added due to cases where the
TaxId value uses another two-letter iso code than the country. IE:
`"GR"` & `"EL"` or `"GB"` and `"XI"`.
- Depending on the tax id value provided, TaxId initializer will route
tp different `TaxIdTypes`. IE: `"SE123456789101"` will resolve to the
`EUVat` while `"GBHA123"` will resolve to `GBVat`.
- Added regexes for EUVats & GBVat

Cargo.toml

@@ -3,4 +3,6 @@ name = "tax_ids"
 version = "0.1.0"
 edition = "2021"
 
-[dependencies]
+[dependencies]
+lazy_static = "1.4.0"
+regex = "1.10.4"