Reader: validate .rela.plt and DT_PLT* consistency

[katsyoshi]

Parent: #39

Scope:

• Validate .rela.plt entry range within PT_LOAD
• Validate relocation type is R_X86_64_JUMP_SLOT for .rela.plt entries
• Validate DT_JMPREL/DT_PLTREL/DT_PLTRELSZ/DT_PLTGOT consistency against section layout
• Ensure linker tests assert via Reader helper

Status: implemented in PR #40.

[katsyoshi]

Completed in PR #40.