Continuous masking of masked variables above 4KiB

Problem

In !2979 (merged), we introduced a fix for masked variables above 4KiB, but it involved sometimes tailing the end of the variable. We discovered this was not a breaking change, as the previous masking implementation would also occasionally reveal masked variables, but in full, at any length, based on how a log line could be split across multiple Write() calls non-deterministically.

Proposal:

Remove the phrase transform and reliance on text/transform which has an internal 4 KiB buffer. This can be done keeping track of how much of a phrase has been matched, instead of buffering the phrase until a match.

Additionally, explore a trie-based solution, but may be difficult because we need to mask over arbitary write boundaries.

Tasks

• New masking solution: !3482
• Conduct regression testing
• Conduct performance testing