[YCQL] LexProcessor should only keep min buffer around in pool

[karan-yb]

Jira Link: DB-7340

Description

LexProcessors are pooled as part of Parser pooling at CQLService level. If there is a query which has large literal value, then we end up increasing the temporary literal buffer size to literal size. The temporary buffer size will remain same until the Lex processor is destroyed. To avoid this large untracked memory, we should reduce the memory usage to min buffer size i.e. 4K before releasing the processor/parser to pool.

Warning: Please confirm that this issue does not contain any sensitive information

• I confirm this issue does not contain any sensitive information.