fix: improve slurp() robustness with size limit and read loop

[imichaelmoore]

Several issues in slurp():

1. No size limit - A large dependency file could exhaust memory
2. Partial reads - read() can return fewer bytes than requested; the code treated this as an error
3. EINTR - Interrupted system calls weren't retried

Fix:

• Add 10MB size limit (SLURP_MAX_SIZE)
• Read in a loop until all bytes are received
• Retry on EINTR
• Log malloc failures

[troydhanson]

Can you rebase this and resolve the conflict?