Summary

Second split-out draft from the large Prisma Client performance branch.

This PR keeps the parser/request-handler allocation reductions that are local to query request parsing and JSON protocol adaptation:

• reduce query parser argument cloning
• avoid input object schema map allocation
• avoid parsed argument value cloning
• avoid eager argument conversion error construction
• avoid empty exclusion vector allocation
• use mutable query parser paths
• use SmallVec for parser validation paths
• collect selection exclusions inline in the JSON protocol adapter
• consume singleton parsed values instead of cloning them

Relation To Larger Work

Parent status PR: #5820

Prior extracted PR: #5821

This branch is independent of the sibling Prisma runtime branch and does not need /prisma-branch.

Scope

Changed files:

• query-compiler/core/src/query_document/parse_ast.rs
• query-compiler/core/src/query_document/parser.rs
• query-compiler/request-handlers/src/protocols/json/body.rs
• query-compiler/request-handlers/src/protocols/json/protocol_adapter.rs

This PR intentionally does not include compact query-plan format changes, raw-nested read plans, or write-graph pruning.

Validation

• cargo check -p query-core: passed
• cargo check -p request-handlers: passed
• cargo check -p query-compiler: passed
• CARGO_TARGET_DIR=/home/aqrln.guest/prisma/.tmp/parser-request-target cargo test -p query-compiler --test queries: passed

The explicit CARGO_TARGET_DIR avoids the local /tmp quota that was hit during the first test attempt.