Optimize diffing

[kerams]

Taking advantage of the fact that the compiler can deduplicate struct DU case fields with the same name and type.

Before

BenchmarkDotNet v0.14.0, Windows 11 (10.0.26100.2894)
AMD Ryzen 9 7900, 1 CPU, 24 logical and 12 physical cores
.NET SDK 9.0.200-preview.0.24575.35
  [Host]     : .NET 9.0.1 (9.0.124.61010), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI DEBUG
  DefaultJob : .NET 9.0.1 (9.0.124.61010), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI

Method	depth	boxed	Mean	Error	StdDev	Gen0	Gen1	Gen2	Allocated
ProcessIncrements	15	False	464.0 ms	7.97 ms	9.18 ms	14000.0000	11000.0000	1000.0000	215.61 MB
ProcessIncrements	15	True	598.1 ms	11.63 ms	12.45 ms	18000.0000	16000.0000	1000.0000	282.03 MB

Method	depth	Mean	Error	StdDev	Gen0	Gen1	Gen2	Allocated
ProcessMessages	10	64.84 ms	0.981 ms	0.917 ms	3250.0000	500.0000	375.0000	53.4 MB
ProcessMessages	15	979.75 ms	19.593 ms	18.327 ms	38000.0000	36000.0000	1000.0000	594.07 MB
CreateWidgets	10	180.9 μs	2.07 μs	1.83 μs	27.3438	22.2168	-	448.23 KB
CreateWidgets	20	67,747.6 μs	1,327.79 μs	1,861.37 μs	4125.0000	4000.0000	750.0000	55342.1 KB

After

Method	depth	boxed	Mean	Error	StdDev	Gen0	Gen1	Gen2	Allocated
ProcessIncrements	15	False	350.1 ms	4.86 ms	4.31 ms	14000.0000	11000.0000	1000.0000	215.61 MB
ProcessIncrements	15	True	516.6 ms	10.31 ms	15.43 ms	18000.0000	16000.0000	1000.0000	282.03 MB

Method	depth	Mean	Error	StdDev	Gen0	Gen1	Gen2	Allocated
ProcessMessages	10	56.67 ms	0.833 ms	0.779 ms	3300.0000	500.0000	400.0000	53.4 MB
ProcessMessages	15	891.50 ms	17.655 ms	20.332 ms	38000.0000	36000.0000	1000.0000	594.07 MB
CreateWidgets	10	178.3 μs	1.42 μs	1.11 μs	27.3438	22.2168	-	448.23 KB
CreateWidgets	20	68,374.6 μs	1,348.72 μs	2,099.80 μs	4125.0000	4000.0000	750.0000	55342.09 KB

[kerams]

This just affects test & bench. The Fabulous project is still pinned to 7.