Improve error message for routing

[mosuem]

Making it a bit less cryptic.

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PR Health

Breaking changes :heavy_check_mark:

Package	Change	Current Version	New Version	Needed Version	Looking good?
code_assets	None	0.19.7	0.19.7	0.19.7	:heavy_check_mark:
data_assets	None	0.19.3	0.19.3	0.19.3	:heavy_check_mark:
hooks	None	0.20.1	0.20.1	0.20.1	:heavy_check_mark:

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Changelog Entry :exclamation:

Package	Changed Files
package:code_assets	pkgs/code_assets/lib/src/code_assets/validation.dart
package:data_assets	pkgs/data_assets/lib/src/data_assets/validation.dart
package:hooks	pkgs/hooks/lib/src/validation.dart

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API leaks :heavy_check_mark:

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

Package	Leaked API symbol	Leaking sources

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License Headers :heavy_check_mark:

// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
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// BSD-style license that can be found in the LICENSE file.

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Files
pkgs/objective_c/lib/src/ns_input_stream.dart

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[dcharkes]

Bump package hooks to 0.19.1-wip.