Speed up WritableBuffer.WriteXxx

[benaadams]

dev

 Method |                       Type |      Mean |    StdDev |       Op/s | Allocated |
------- |--------------------------- |---------- |---------- |----------- |---------- |
 Output |                 LiveAspNet | 3.8515 us | 0.0253 us | 259,636.96 |     664 B |
 Output |           PlaintextChunked | 1.4079 us | 0.0277 us | 710,277.44 |     232 B |
 Output | PlaintextChunkedWithCookie | 2.9045 us | 0.0464 us | 344,288.21 |     814 B |
 Output |        PlaintextWithCookie | 3.4845 us | 0.0525 us | 286,983.30 |     900 B |
 Output |       TechEmpowerPlaintext | 1.8344 us | 0.0136 us | 545,149.42 |     317 B |

PR

 Method |                       Type |      Mean |    StdDev |       Op/s | Allocated |
------- |--------------------------- |---------- |---------- |----------- |---------- |
 Output |                 LiveAspNet | 3.0829 us | 0.0762 us | 324,367.00 |     353 B |
 Output |           PlaintextChunked | 1.2563 us | 0.0075 us | 795,959.04 |     192 B |
 Output | PlaintextChunkedWithCookie | 1.9574 us | 0.0136 us | 510,893.40 |     487 B |
 Output |        PlaintextWithCookie | 2.6213 us | 0.0294 us | 381,491.96 |     573 B |
 Output |       TechEmpowerPlaintext | 1.7388 us | 0.0293 us | 575,102.39 |     277 B |

/cc @davidfowl

[benaadams]

Added benchmarks

[benaadams]

feature-si for reference - still long way to go

 Method |                       Type |          Mean |     StdDev |          RPS | Allocated |
------- |--------------------------- |-------------- |----------- |------------- |---------- |
 Output |                 LiveAspNet | 1,384.3867 ns | 21.0264 ns |   722,341.54 |      64 B |
 Output |           PlaintextChunked |   570.4469 ns |  8.7973 ns | 1,753,011.45 |      64 B |
 Output | PlaintextChunkedWithCookie |   927.3479 ns | 10.3280 ns | 1,078,343.95 |      64 B |
 Output |        PlaintextWithCookie |   953.3636 ns | 12.3276 ns | 1,048,917.75 |      64 B |
 Output |       TechEmpowerPlaintext |   581.0874 ns |  7.2057 ns | 1,720,911.39 |      64 B |

[benaadams]

@davidfowl Benchmark isn't returning blocks, when/how is that supposed to happen (i.e. what hook do I need to add)

[benaadams]

PR

 Method |                       Type |      Mean |    StdDev |      Op/s | Allocated |
------- |--------------------------- |---------- |---------- |---------- |---------- |
 Output |                 LiveAspNet | 2.8919 us | 0.0866 us | 345797.29 |     353 B |
 Output |           PlaintextChunked | 1.2609 us | 0.0103 us | 793106.22 |     192 B |
 Output | PlaintextChunkedWithCookie | 1.9944 us | 0.0231 us | 501415.48 |     487 B |
 Output |        PlaintextWithCookie | 2.2267 us | 0.0186 us | 449097.08 |     509 B |
 Output |       TechEmpowerPlaintext | 1.3983 us | 0.0168 us | 715156.59 |     214 B |