fix: keep REST server adapter out of production dependencies (#4240)

The production `remote` client talks to an existing namespace over HTTP.
It needs `lance-namespace-impls/rest`, not the REST *server* adapter.
`RestAdapter` is only used by `cfg(test)` integration tests that stand
up an in-process server. Enabling `rest-adapter` on the production
`remote` feature pulled that server stack, including Axum 0.7, into
default Python wheels.

This keeps `rest` on `remote` and moves `rest-adapter` to a
`lance-namespace-impls` dev-dependency so those tests still compile and
run. Cargo resolver=2 does not leak the extra feature into
`lancedb-python`.

## Measurement

Paired `maturin build --release --strip --target aarch64-apple-darwin
--features fp16kernels` wheels. Source was `3be29228` plus this
Cargo.toml change, which is this PR's tree (`878b2ae5` on `3be29228`).
Same toolchain, profile, and packaging flags; only `rest-adapter` moved.

| Artifact | Before | After | Delta |
| --- | ---: | ---: | ---: |
| Compressed wheel | 64,685,664 | 63,824,281 | −861,383 (−1.33%) |
| `_lancedb.abi3.so` uncompressed | 148,255,440 | 146,275,936 |
−1,979,504 (−1.34%) |

This is macOS arm64, not Windows. It does not resolve the Windows wheel
upload limit. Tonic still pulls Axum 0.8; the change only removes the
adapter's Axum 0.7 stack from the production graph.

rust/lancedb/Cargo.toml

@@ -106,6 +106,9 @@ sha2 = "0.10"
 [dev-dependencies]
 anyhow = "1"
 lance-testing = { workspace = true }
+# RestAdapter is only used by cfg(test) code. Keep rest-adapter off the
+# production remote feature so Python wheels do not resolve its Axum 0.7 stack.
+lance-namespace-impls = { workspace = true, features = ["rest-adapter"] }
 tempfile = { workspace = true }
 random_word = { version = "0.4.3", features = ["en"] }
 tokio = { workspace = true, features = ["io-util", "macros", "net", "test-util"] }
@@ -169,7 +172,6 @@ remote = [
     "dep:webbrowser",
     "dep:fs4",
     "lance-namespace-impls/rest",
-    "lance-namespace-impls/rest-adapter",
 ]
 # Publish LanceDB's internal metrics (currently object store request counts,
 # bytes, latency, errors, and throttles) through the `metrics` crate facade,