Add string start addresses to -strings output

[kami922]

Closes #99

Summary

• Added StringEntry struct (Str string, Start uint64) to objfile/strings.go — replaces bare string in the output
• ExtractStrings() now returns []StringEntry instead of []string; the start VA comes directly from c.Pointer which was already computed during blob walking
• Updated ExtractMetadata.Strings in main.go from []string to []objfile.StringEntry
• -human output now prints 0x<addr> <string> per entry
• Added StringEntry message to GoReSym.proto; changed repeated string strings → repeated StringEntry strings
• Tests updated to use .Str field and assert Start != 0 for every extracted string

Example output change

Before:

"Strings": ["main", "runtime.goexit"]

After:

"Strings": [{"Str": "main", "Start": 4890624}, {"Str": "runtime.goexit", "Start": 4891136}]

Notes

• Only Start is included per Steve's guidance — consumers can derive End from Start + len(Str)
• Deduplication by string value is preserved; all candidates referencing the same string point to the same blob offset so the captured address is always correct
• No new dependencies introduced

🤖 Generated with Claude Code

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[stevemk14ebr]

The implementation looks good here, CI error suggests a test needs updated however

[stevemk14ebr]

thanks!