fix(api): parameterized FromRow methods (fetch_*_as_params / stream_as_params)

[StefanSteiner]

Summary

Adds the missing intersection of FromRow struct-mapping and ToSqlParam
parameter binding (issue #137). Before this, you could map rows into a struct
(fetch_*_as / stream_as, plain &str queries) or bind $N parameters
(query_params, raw Rows) — but not both in one call. A parameterized
SELECT … WHERE org_id = $1 you wanted as a Vec<User> forced a manual
RowAccessor/row.get() loop.

New _as_params trio on both Connection and AsyncConnection:

• fetch_one_as_params::<T>(query, params) -> Result<T>
• fetch_all_as_params::<T>(query, params) -> Result<Vec<T>>
• stream_as_params::<T>(query, params) -> Result<impl Iterator<Item = Result<T>>>
  (async: impl Stream<Item = Result<T>>, no outer Result)

#[derive(hyperdb_api_derive::FromRow)]
struct User { id: i32, name: String }

let users: Vec<User> = conn.fetch_all_as_params(
    "SELECT id, name FROM users WHERE org_id = $1",
    &[&42i32],
)?;

Design

The two halves already existed — this plumbs them together.

• Sync (all 3) + async fetch_one_as_params / fetch_all_as_params delegate to
  query_params, which already returns a Rowset/AsyncRowset carrying the
  prepared-statement guard. TypedRowIterator::new takes the whole rowset, so
  Drop ordering (close_statement after the rowset releases its connection
  lock) is preserved with no extra code. Rows are mapped exactly as the existing
  *_as methods (build_indices once + FromRow::from_row per row).
• Async stream_as_params is the exception: &[&dyn ToSqlParam] can't cross the
  try_stream! await points, so it encodes params up front (encoding needs no
  connection) and rebuilds query_params' Parse/Bind/Execute sequence inline,
  carrying the statement guard. The Prepared path exposes its schema at prepare
  time, so the column-index map is built once up front. A "keep in sync with
  query_params" comment marks the duplication.

Naming: _as_params composes the two existing axes (_as = map to struct,
_params = bind params) in their established reading order. Both plan reviewers
endorsed it over _params_as.

Error semantics

• fetch_one_as_params returns "Query returned no rows" on empty results
  (same as fetch_one_as).
• Sync stream_as_params surfaces stream-open errors — including
  FeatureNotSupported on gRPC (prepared statements are TCP-only) — on the
  outer Result; per-row mapping errors come back as each item's Result.
• Async stream_as_params has no outer Result, so submission failures
  (incl. the gRPC FeatureNotSupported) surface as the first yielded Err item.

Docs & examples

• FromRow and ToSqlParam rustdoc cross-reference the new methods.
• row_mapping_forms example gains Form 6 (verified end-to-end).
• docs/ROW_MAPPING.md: new "Form 6 — Parameterized struct mapping" section +
  Choosing-a-form row; retitled "Six Forms".
• README: note + snippet under Parameterized Queries.
• Bonus: fixed stale async query_params rustdoc that described "text-mode
  escaping" — it has done binary Parse/Bind/Execute since the async-parity work.

Out of scope (deliberate)

• Node bindings — additive Rust-only convenience methods; N-API surface is
  opt-in per binding, so adding Rust methods doesn't auto-expose them.
• compile-check crate — unaffected (plain inherent methods, no derive/version-gate interaction).
• gRPC error-path tests — pre-existing gap shared with query_params; not widened here.

Test plan

• cargo clippy --workspace --all-targets -- -D warnings — clean
• cargo test -p hyperdb-api — full suite green (8 new tests: 5 sync + 3 async)
• cargo test -p hyperdb-api --doc — 171 passed
• cargo run -p hyperdb-api --example row_mapping_forms — Form 6 filters price < $15 → 3 rows
• cargo build --workspace — green

Acceptance criteria (#137)

• Sync + async variants for fetch_one / fetch_all / stream.
• Round-trip test: $1-bound ToSqlParam → #[derive(FromRow)] struct,
  asserting values (plus multi-param and empty-result edge cases).
• Docs/examples updated; FromRow and ToSqlParam module docs
  cross-reference the new methods.

Closes #137.