[PM-5692] Extract generators to separate crate

[Hinton]

Type of change

- [ ] Bug fix
- [ ] New feature development
- [x] Tech debt (refactoring, code cleanup, dependency upgrades, etc)
- [ ] Build/deploy pipeline (DevOps)
- [ ] Other

Objective

Continuation on #402. This PR extracts the generators to their own crate to establish clear boundaries between the code. There is still some logic in the client to expose generators that we may want to revisit.

Also extracts explicit errors for the different generators for better error handling downstream when/if desired.

Before you submit

• Please add unit tests where it makes sense to do so

[codecov]

Codecov Report

Attention: 96 lines in your changes are missing coverage. Please review.

Comparison is base (d2cb4f9) 50.19% compared to head (f1d2157) 50.51%.
Report is 4 commits behind head on main.

Files	Patch %	Lines
...generators/src/username_forwarders/forwardemail.rs	84.97%	26 Missing ⚠️
...den-generators/src/username_forwarders/fastmail.rs	70.21%	14 Missing ⚠️
crates/bitwarden-uniffi/src/crypto.rs	0.00%	10 Missing ⚠️
...-generators/src/username_forwarders/simplelogin.rs	90.32%	9 Missing ⚠️
crates/bitwarden-generators/src/username.rs	11.11%	8 Missing ⚠️
crates/bitwarden-generators/src/passphrase.rs	12.50%	7 Missing ⚠️
crates/bitwarden-generators/src/password.rs	16.66%	5 Missing ⚠️
...arden-generators/src/username_forwarders/addyio.rs	97.50%	3 Missing ⚠️
...n-generators/src/username_forwarders/duckduckgo.rs	90.00%	3 Missing ⚠️
crates/bitwarden/src/mobile/client_crypto.rs	0.00%	3 Missing ⚠️
... and 4 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #511      +/-   ##
==========================================
+ Coverage   50.19%   50.51%   +0.32%     
==========================================
  Files         157      159       +2     
  Lines        7493     7625     +132     
==========================================
+ Hits         3761     3852      +91     
- Misses       3732     3773      +41     

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