engines/dotnet: make it more idiomatic and improve perf

Performance updates:

* Use EnumerateMatches instead of Matches when capture groups aren't
needed.
* Use Match w/ NextMatch instead of Matches when capture groups are
needed.
* Use EnumerateLines to avoid materializing strings for each line when
not necessary.

Idiom updates:

* Use switch statements/expressions instead of large cascading
if/elses.
* Use and slice spans instead of `List<byte>` manipulations.
* No need to explicitly use Stream.Read; it can instead copy the
input stream to a memory stream and get a span to the memory stream's
buffered data.
* Change comments to be structured XML comments so that they show up
for consumers in IntelliSense / docs / etc.
* Use Elapsed.TotalNanoseconds instead of a custom helper.
* Use Func<..> instead of custom delegates.
* Use ++ instead of += 1.
* Use record structs for simple POCOs.

Closes #10

benchmarks/engines.toml

@@ -277,15 +277,15 @@
  name = "dotnet"
  cwd = "../engines/dotnet"
  [engine.version]
- bin = "bin/Release/net7.0/main"
+ bin = "bin/Release/net8.0/main"
  args = ["version"]
  [engine.run]
- bin = "bin/Release/net7.0/main"
+ bin = "bin/Release/net8.0/main"
  args = ["interp"]
  [[engine.dependency]]
  bin = "dotnet"
  args = ["--list-sdks"]
- regex = '(?m)^7\.'
+ regex = '(?m)^8\.'
  [[engine.build]]
  bin = "dotnet"
  args = ["build", "-c", "Release"]
@@ -302,15 +302,15 @@
  name = "dotnet/compiled"
  cwd = "../engines/dotnet"
  [engine.version]
- bin = "bin/Release/net7.0/main"
+ bin = "bin/Release/net8.0/main"
  args = ["version"]
  [engine.run]
- bin = "bin/Release/net7.0/main"
+ bin = "bin/Release/net8.0/main"
  args = ["compiled"]
  [[engine.dependency]]
  bin = "dotnet"
  args = ["--list-sdks"]
- regex = '(?m)^7\.'
+ regex = '(?m)^8\.'
  [[engine.build]]
  bin = "dotnet"
  args = ["build", "-c", "Release"]
@@ -329,15 +329,15 @@
  name = "dotnet/nobacktrack"
  cwd = "../engines/dotnet"
  [engine.version]
- bin = "bin/Release/net7.0/main"
+ bin = "bin/Release/net8.0/main"
  args = ["version"]
  [engine.run]
- bin = "bin/Release/net7.0/main"
+ bin = "bin/Release/net8.0/main"
  args = ["nobacktrack"]
  [[engine.dependency]]
  bin = "dotnet"
  args = ["--list-sdks"]
- regex = '(?m)^7\.'
+ regex = '(?m)^8\.'
  [[engine.build]]
  bin = "dotnet"
  args = ["build", "-c", "Release"]