Rollup merge of #62164 - jsgf:buffer-save-analysis, r=Xanewok
Rollup merge of #62164 - jsgf:buffer-save-analysis, r=Xanewok

save-analysis: use buffered writes

Otherwise it ends up writing the file byte at a time, which can be very slow for large outputs.

cc @ljw1004

aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust