ToSqlParam for Geography: blocked on binary bind (needs text-format param bind)

[StefanSteiner]

Summary

impl ToSqlParam for Geography (a sub-item of #65) is not implementable over
the current bind path: Hyper has no PostgreSQL-binary input function for the
geography type, and query_params sends every parameter as PG binary
(format code 1, hardcoded). This issue tracks adding geography query-parameter
support once a text-format bind path exists.

Evidence (probed against hyperd 0.0.25080)

Binding a geography param via query_params was tried with three candidate
binary encodings — raw stored bytes (Geography::as_bytes), WKB
(Geography::to_wkb), and the HyperBinary [u32_le len][data] form
(ToHyperBinary). All three fail identically at Bind/Execute:

ERROR: no pg binary input function available for type geography (42883)

This is not an encoding bug — Hyper simply has no binary input decoder for
geography. Because the bind path is binary-only
(hyperdb-api-core/src/client/connection.rs:517, param_formats = vec![1; n]),
there is no byte sequence that makes a geography param work today.

What DID ship for geography in #65

The Inserter path (COPY / HyperBinary, a different channel) works fine, so
#65's commit added impl IntoValue for Geography + Inserter::add_geography,
verified by a round-trip test (raw bytes in → byte-identical out). Only the
query-parameter (ToSqlParam) direction is blocked.

Path to support

Same root cause and fix as #132 (scaled Numeric params): allow per-parameter
text-format bind (format code 0) instead of the current uniform binary.
Geography has a text input function (WKT), so a text-bound geography param
($1 carrying WKT bytes, oid = geography) should parse. Requires plumbing
per-parameter format codes through start_execute_prepared / frontend::bind.

Acceptance criteria

• A Geography can be passed to query_params and used in a predicate /
  projection (e.g. SELECT ST_Distance($1, g) FROM ...).
• Round-trips correctly (WKT in → same geometry out).

Related

• ToSqlParam coverage: Numeric, Interval, Geography, JSON #65 — added IntoValue for Geography; this is the remaining ToSqlParam half.
• ToSqlParam: support scaled Numeric (scale > 0) params — needs text-format bind #132 — scaled Numeric params; same per-parameter-text-format-bind fix unblocks both.