docs: update models.md with missing fields

[mahek56]

Updated docs/models.md to include missing fields for the following models:

• Contrato: added numero_controle_pncp, numero_controle_pncp_compra,
  numero_controle_pncp_ata, informacao_complementar, data_atualizacao_global
• Contratacao: added modalidade_id, data_atualizacao_global
• Ata: added numero_controle_pncp_ata, numero_controle_pncp_compra,
  situacao, unidade_nome, orgao_uf, data_atualizacao_global
• SearchResult: added id, numero_controle_pncp, numero_sequencial,
  tipo_nome, tipo_contrato_nome, exigencia_conteudo_nacional
• ItemCompra: added tipo, tipo_nome

Closes #3

[gabrielgz0]

Hi @mahek56, thanks for the contribution. The PR looks great. You covered all the fields from issue #3. Clean diff, only the right file was modified.

Two small corrections from the source code:

1. Ata.orgao_uf wrong alias
Code at src/pypncp/models.py:288:
orgao_uf: str | None = None
No Field, no alias. ufSigla does not exist for this field. Remove the alias column or leave it blank.

2. SearchResult.numero_sequencial wrong type
Code at src/pypncp/models.py:328:
numero_sequencial: str = Field(default="", alias="numero_sequencial")
It is str, not int | None. Default is an empty string.

Other than that, its perfect. Fix these two and I will approve.