Add configurable MaximumReadableBytes via HttpResponseFormatterOptions

[adrianiftode]

Closes #167

What

Makes the content truncation limit (MaximumReadableBytes) configurable, without breaking existing users:

• Per call — new parameter object HttpResponseFormatterOptions on HttpMessageFormatter:

var formatted = response.Format(new HttpResponseFormatterOptions
{
    MaximumReadableBytes = 4 * 1024
});

• Globally — new ResponseFormatterOptions on FluentAssertionsWebConfig / AwesomeAssertionsWebConfig, set the same way as the existing Serializer setting:

FluentAssertionsWebConfig.ResponseFormatterOptions = new HttpResponseFormatterOptions
{
    MaximumReadableBytes = 4 * 1024
};

Why

The limit was a hard-coded const (10 * 128 * 1024) in ContentFormatterOptions, so users had no way to print more (or less) of a large response in their assertion failure messages.

How

• HttpResponseFormatterOptions is a public parameter object with MaximumReadableBytes (defaults to the previous const value, must be > 0).
• The parameter is exposed as an additional Format overload rather than an optional parameter on the existing method, so the change is both source- and binary-compatible — response.Format() keeps working untouched.
• The options are threaded through the formatting pipeline (Appender → ProcessorsRunner → content processors → ProcessorBase.AppendContentWithinLimits), including multipart parts.
• HttpMessageFormatter itself keeps no global state. The global lives only in FluentAssertionsWebConfig (and AwesomeAssertionsWebConfig via the AAV link-compiled source) and is read by the HttpResponseMessageFormatter adapter when it renders assertion failure messages. The *.Web.Types projects now reference HttpMessageFormatter.
• InternalServerErrorProcessor still bypasses the limit, exactly as before.

Tests

• HttpMessageFormatter.Tests: truncation with a custom limit through Format(options), defaults unchanged, invalid values throw, plus processor-level coverage.
• FluentAssertions.Web.FluentAssertionsWebConfig.Tests and AwesomeAssertions.Web.AwesomeAssertionsWebConfig.Tests: default value and the global option limiting the formatted failure message (save/restore via IDisposable, non-parallelized collection).

Full solution builds with 0 errors, all tests pass on net9.0/net10.0 for the FluentAssertions.Web, .v8 and AwesomeAssertions flavors, and dotnet pack succeeds. Docs updated in the package readme and the root readme.