Optimize class method field fast paths

[TheHypnoo]

Summary

• Add a direct class-method shape guard for statically safe method calls so the hot path avoids typed-feedback site bookkeeping when no instance field can shadow the method.
• Lower safe PutValueSet class-field writes to the existing direct PropertySet path, including this.field = ... inside class methods.
• Add typed-feedback-disabled fast contracts for class-field get/set guards to avoid expensive observation/key/descriptor work in normal runs while preserving the full guard when descriptors or prototype fast-guard invalidation are active.

Performance

benchmarks/suite/09_method_calls.ts (--no-auto-optimize, 7 samples):

Runtime	Median
Perry	229 ms
Node	11 ms
Bun	20 ms

Previous Perry median on the stacked base was ~6,089 ms, so this is about 26.6x faster for the current bottleneck while preserving the expected output (value:10000000).

Validation

• rustfmt --check on touched files
• cargo check -p perry-codegen --quiet
• cargo test -p perry-runtime typed_feedback --quiet
• cargo build -p perry --release --quiet
• Perry/Node output comparison for test-files/test_issue_620.ts