feat(sql): bind typed parameters across database clients

[slepp]

Why

SQL parameters were newline-delimited bytes. A multiline value became several parameters, and applications could not bind NULL, booleans or binary data reliably.

What

Add hew.db.sql.Param with Null, Bool, Int, Float, Text and Bytes variants. SQLite, MySQL and PostgreSQL accept Vec<Param>, use Hew's wire codec internally and bind native typed values. PostgreSQL prepares typed parameters instead of coercing every input to text. Empty values remain distinct from NULL.

Test

• Execute the three Hew integration suites against SQLite, MySQL and PostgreSQL, including multiline Unicode text, arbitrary bytes, NULL, booleans, integer limits, floats, empty values and parameter-count errors.
• Run native crate tests, all ecosystem source checks, the package contract and make lint.
• Exercise a multiline blog post through HTTP and confirm exact SQLite persistence; import CSV values containing newlines, Unicode and quoted identifiers into PostgreSQL.