feat: add first-class function wire contracts (#3985)

## Problem

Enterprise Function-backed computed columns need a stable SDK contract
before Sophon catalog and execution endpoints can be added. The existing
`Job` API can only represent unit terminal results, and there is no
shared Rust/Python wire definition for immutable Function versions,
applications, bindings, or refresh results.

## Behavior

This introduces remote-only canonical Function values in Rust and
Python, evolves `Job<T = ()>` to decode typed remote terminal results
while keeping local spawned operations unit-typed, and fixes the
cross-language contract with shared JSON golden fixtures. Unknown fields
and discriminator values remain forward-decodable, while canonical
output contains only fields known to the client. Function models contain
secret names only.

Sophon remains the sole owner of catalog persistence, environment bake,
secret resolution, execution, and publication. This PR does not add
authoring/catalog endpoints, local execution, refresh runners, or live
Sophon E2E coverage.

docs/src/python/python.md

@@ -54,6 +54,42 @@ listing a storage directory.
 
 ::: lancedb.LsmWriteSpec
 
+## Functions and Jobs
+
+::: lancedb.functions.FunctionArtifact
+
+::: lancedb.functions.FunctionParameter
+
+::: lancedb.functions.FunctionResultField
+
+::: lancedb.functions.FunctionOutput
+
+::: lancedb.functions.FunctionSignature
+
+::: lancedb.functions.PythonEnvironmentSpec
+
+::: lancedb.functions.FunctionVersion
+
+::: lancedb.functions.PythonRuntimeSpec
+
+::: lancedb.functions.FunctionVersionRef
+
+::: lancedb.functions.ApplicationInput
+
+::: lancedb.functions.FunctionApplication
+
+::: lancedb.functions.InputBinding
+
+::: lancedb.functions.OutputMapping
+
+::: lancedb.functions.FunctionBinding
+
+::: lancedb.functions.RefreshColumnResult
+
+::: lancedb.job.Job
+
+::: lancedb.job.AsyncJob
+
 ## Expressions
 
 Type-safe expression builder for filters and projections. Use these instead
@@ -153,8 +189,9 @@ The same option is available on `lancedb.tokenize(...)` and the deprecated
 ```python
 import lancedb
 
-tokens = list(lancedb.tokenize("acme makes searchable data",
-                               custom_stop_words=["acme"]))
+tokens = list(
+    lancedb.tokenize("acme makes searchable data", custom_stop_words=["acme"])
+)
 ```
 
 ::: lancedb.tokenize