Allow downscaling image in GetScreenshot inspection request (#8248)

When an agent screenshots the app using the mcp and then interacts with
the app by clicking at coords, they see the coords in the native image
coords. Since the mcp does everything else in logical coordinates, it
helps if the image they see is also in logical resoltution, so we always
downscale it to 1.0.

I've added this here to avioid having to decode and re-encode the image
in the mcp.
Unfortunately it only does downscaling for now, since adding some way to
upscale the image just for the screenshot would add a lot of complexity,
and might be invasive from a plugin.

I've also changed the submit call to take a closure, to make it easier
to use other transport channel (makes the implementation for reruns mcp
nicer).

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Co-authored-by: Lucas Meurer <lucas@rerun.io>

Cargo.lock

@@ -4859,9 +4859,9 @@ dependencies = [
 
 [[package]]
 name = "tracing"
-version = "0.1.40"
+version = "0.1.44"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c3523ab5a71916ccf420eebdf5521fcef02141234bbc0b8a49f2fdc4544364ef"
+checksum = "63e71662fa4b2a2c3a26f570f037eb95bb1f85397f3cd8076caed2f026a6d100"
 dependencies = [
  "pin-project-lite",
  "tracing-attributes",
@@ -4870,9 +4870,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-attributes"
-version = "0.1.27"
+version = "0.1.31"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "34704c8d6ebcbc939824180af020566b01a7c01f80641264eba0999f6c2b6be7"
+checksum = "7490cfa5ec963746568740651ac6781f701c9c5ea257c58e057f3ba8cf69e8da"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -4881,9 +4881,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-core"
-version = "0.1.32"
+version = "0.1.36"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c06d3da6113f116aaee68e4d601191614c9053067f9ab7f6edbcb161237daa54"
+checksum = "db97caf9d906fbde555dd62fa95ddba9eecfd14cb388e4f491a66d74cd5fb79a"
 dependencies = [
  "once_cell",
 ]