refactor: change build strategy to merge

[negarciacamilo]

Description

Se mergean todos los pkg en uno solo para performance

[danteay]

LGTM -- solid refactor that replaces the concurrent multi-process mockery strategy with a single merged invocation. The ~270 net lines removed (concurrency plumbing, goroutine pool, semaphore, progress channels) are replaced by a much simpler merge-then-execute-once approach. CI checks pass.

A few non-blocking suggestions:

1. Potential temp file leak on createSingleTempConfig failure
In Exec(), defer m.cleanup() is declared after createSingleTempConfig() returns. If that function partially writes a temp file (it appends to m.tmpFiles before returning) and then fails, the defer is never registered. Consider moving defer m.cleanup() earlier in Exec(), e.g., right before the merge/create calls.

2. Redundant doneChan in runSingleInvocation
Both the spinner path (spin.Action(...).Run()) and the non-TTY path are synchronous, so <-doneChan is always a no-op by the time it's reached. The channel + goroutine pattern could be simplified by removing doneChan entirely and calling the work function directly.

3. Empty packages edge case
If all package configs lack a packages key (or it's not a map), mergeSingleConfig returns a config with no packages. Mockery will run with nothing to do. A warning or early return might be helpful.

4. Backward compatibility of --jobs-num removal
Worth verifying that no CI scripts or Makefiles in consuming repos pass --jobs-num / -j, as they would break with an "unknown flag" error.

Overall this is a clean improvement. Nice work.

[danteay]

Second review pass -- all four suggestions from the first review have been properly addressed:

1. Temp file leak -- defer m.cleanup() is now placed before createSingleTempConfig() with an explanatory comment. Correct.
2. Redundant doneChan -- Entire channel/goroutine pattern removed. runSingleInvocation now calls work synchronously in both TTY and non-TTY paths. Clean.
3. Empty packages edge case -- Explicit hasPackages check with warning and early return added after mergeSingleConfig. Correct.
4. --jobs-num backward compatibility -- Acknowledged as a coordination concern, not a code defect.

Code quality is solid:

• mergeSingleConfig correctly deep-merges duplicate package definitions so interfaces from multiple configs are preserved.
• The overall flow in Exec() reads linearly and is easy to follow.
• CI checks pass (lint + commit_lint).

Approving.