Fix URL encoding of route values in routeless test helpers

[Benziza]

Summary

URL-encode hydrated route parameter values generated by GetTestUrlFor().

Route values containing reserved URI characters such as #, ?, or spaces are currently inserted directly into the generated URL. This can truncate or alter the request before it reaches the endpoint.

Reproduction

Given the following route:

Get("/items/{name}");

And this request value:

Name = "part#1?x y";

GetTestUrlFor() currently generates:

items/part#1?x y

The actual request path becomes:

/items/part

Fix

Encode hydrated route parameter values with Uri.EscapeDataString() while preserving unresolved route placeholders.

Catch-all route handling is intentionally outside the scope of this change.

Tests

• HttpClientExtensionsTests: 12/12 passed
• Unit.FastEndpoints: 346/346 passed
• Full solution build: 0 warnings and 0 errors

[Benziza]

Companion documentation PR: FastEndpoints/Documentation#40