Fix spurious line breaks in pretty-printing of qualified module paths

[JNC4]

Summary

• Remove the @, (break hint) from the format string in pp_msymbol when printing multi-component module paths
• The break hint allowed OCaml's Format module to insert line breaks between namespace components (e.g., between G. and RO), producing incorrect output

Before:

proc sample(x : G.in_t) : unit = {
    G.
    RO.get(x);
}

module Alias = G.
RO.

After:

proc sample(x : G.in_t) : unit = {
    G.RO.get(x);
}

module Alias = G.RO.

Test plan

• Reproduced the bug using the exact example from Newline in pretty printing modules with namespaces #696
• Verified fix resolves both manifestations (procedure call and module alias)
• All 40 unit tests pass
• Builds cleanly

Fixes #696.

[strub]

Note that the way that hint is used by Format indicates that the procedure call is printed with a vertical box, something that we might want to avoid.

Anyway, since the parser does not support namespace with spaces, the hint is invalid.