Crash fix paging

[michaelortmann]

Found by: https://github.com/michaelortmann/
Patch by: https://github.com/michaelortmann/
Fixes: #1762

One-line summary:

Additional description (if needed):
get_data_ptr() -> n_malloc() could destroy line, so copy line to line_r to make append_line() reentrant
Turn paging off before booting a user in case of too many page lines to avoid infinite loop
Rise max page lines from 1000 to 2000
Add tcl command doc for tcl_page
Remember: If user is for example HQ, then do_boot() will automatically re-login, and set the console page status to the value stored in console mod, if that mod is loaded, eventually triggering an infinite loop / segfault.
In addition to finding the bug in February 2025 with #1762, and fixing it, i have now also been able to automatically find it flexing https://github.com/AFLplusplus/AFLplusplus

Test cases demonstrating functionality (if applicable):
Create a motd with 1003 lines

> wc -l text/motd
1003 text/motd

log in with HQ, like with ./eggdrop -t eggdrop.conf

.page 5
.motd
[...]
`Segmentation fault         (core dumped) ./eggdrop -t BotA.conf`

This was only one example to trigger the bug. Another one is having many ignores and doing the following will crash the bot:

.page 5
.ignores

[thommey]

LGTM